by R. W. Pride, F. W. Meyer, and R. N. Cherry, prepared by the United States Geological Survey in cooperation with the Florida Geological Survey, the Florida Division of Water Resources and Conservation, and the Southwest Florida Water Management District

The author dedicated the work to the public domain by waiving all of his or her rights to the work worldwide under copyright law and all related or neighboring legal rights he or she had in the work, to the extent allowable by law.

The Florida Geological Survey holds all rights to the source text of
this electronic resource on behalf of the State of Florida. The
Florida Geological Survey shall be considered the copyright holder
for the text of this publication.

Under the Statutes of the State of Florida (FS 257.05; 257.105, and
377.075), the Florida Geologic Survey (Tallahassee, FL), publisher of
the Florida Geologic Survey, as a division of state government,
makes its documents public (i.e., published) and extends to the
state's official agencies and libraries, including the University of
Florida's Smathers Libraries, rights of reproduction.

The Florida Geological Survey has made its publications available to
the University of Florida, on behalf of the State University System of
Florida, for the purpose of digitization and Internet distribution.

The Florida Geological Survey reserves all rights to its publications.
All uses, excluding those made under "fair use" provisions of U.S.
copyright legislation (U.S. Code, Title 17, Section 107), are
restricted. Contact the Florida Geological Survey for additional
information and permissions.

STATE OF FLORIDA
STATE BOARD OF CONSERVATION
DIVISION OF GEOLOGY

FLORIDA GEOLOGICAL SURVEY
Robert O. Vernon, Director

REPORT OF INVESTIGATIONS NO. 42

HYDROLOGY OF GREEN SWAMP AREA IN
CENTRAL FLORIDA

By
R. W. Pride, F. W. Meyer, and R. N. Cherry

Prepared by the
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
FLORIDA GEOLOGICAL SURVEY,
the
FLORIDA DIVISION OF WATER RESOURCES AND CONSERVATION,
and the
SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT

Dear Governor Burns:
For many years, it has been thought that much of the recharge
of water to Florida's prolific artesian aquifer occurred in the Green
Swamp area. For this reason, it was believed that a detailed geo-
logic and hydrologic study of the area would be helpful and neces-
sary. I am pleased to report to you that a study, "Hydrology of
Green Swamp Area in Central Florida," prepared by R. W. Pride,
F. W. Meyer, and R. N. Cherry, of the U. S. Geological Survey, in
cooperation with the Division of Geology of the State Board of
Conservation, will be published as Florida Geological Survey Re-
port of Investigations No. 42.
This report provides all of the data necessary for the wise utili-
zation, and perhaps for the preservation, of parts of the Green
Swamp area. It will also assist in the planning for the Four-
Rivers area to alleviate floods and to conserve our water and land.

Respectfully yours,
Robert O. Vernon
Director and State Geologist

Completed manuscript received
September 9, 1965

Published for the Florida Geological Survey
By the E. O. Painter Printing Company
DeLand, Florida

This report was prepared by the Water Resources Division of
the U. S. Geological Survey in Cooperation with the Florida
Geological Survey, the Florida Division of Water Resources and
Conservation, and the Southwest Florida Water Management
District.
The authors wish to express their appreciation for the
cooperation of the many residents and public officials for
information given during the well inventory and reconnaissance
of the area. Special acknowledgement is due the Florida State
Road Department, the Florida Forest Service, and property owners
who granted permission to drill test wells. The following agencies
made financial contributions for the collecting of data used in this
report: Hillsborough County, Marion County, Pasco County, Polk
County, Sumter County, Lake Apopka Recreation and Water
Conservation Control Authority, Oklawaha Basin Recreation and
Water Conservation and Control Authority, and Tsala Apopka
Basin Recreation and Water Conservation Control Authority.
The calcium carbonate equilibrium study of ground water of
central Florida was based on data collected and analysed in
cooperation with William Back, Geologist, Water Resources
Division, Arlington, Virginia, as part of an investigation of ground
water along the Atlantic seaboard. Contributions to the knowledge
of the geohydrology in the Withlacoochee-Hillsborough overflow
area were made by Z. S. Altschuler, Geologist, Geologic Division,
Washington, D. C. Assistance in the interpretation of electric and
drillers' logs was rendered by C. R. Sproul, Geologist, Florida
Geological Survey.
The work on this project was done under the supervision of
the Florida Water Resources Division Council comprised of A. O.
Patterson, district engineer of the Branch of Surface Water, M. I.
Rorabaugh, succeeded by C. S. Conover, district engineers of the
Branch of Ground Water, and J. W. Geurin, district chemist,
succeeded by K. A. MacKichan, district engineer, of the Branch of
Quality of Water.

Green Swamp is an area of about 870 square miles of swampy
flatlands and sandy ridges near the center of the Florida Peninsula.
The elevation of the land surface ranges from about 200 feet above
mean sea level in the eastern part to about 75 feet in the western
part. The Withlacoochee River drains two-thirds of the area. The
Little Withlacoochee River, the headwaters of the Oklawaha River,
the Hillsborough River, the headwaters of the Kissimmee River,
and the headwaters of Peace River drain the remaining area. The
surface is mantled with a varying thickness of sand and clay which
comprises the nonartesian aquifer. Porous marine limestones
comprising the Floridan aquifer underlie and drain the subsurface.
The Floridan aquifer crops out in the western part of the area and
occurs at depths ranging from 50 to more than 200 feet in the
eastern part. The mineral content of both surface and ground
water does not impair the usability of the water for most purposes.
However, surface water is generally highly colored and acidic, and
ground water is hard and generally contains objectionable amounts
of iron.
Hydrologic data were collected during the period, July 1, 1958,
to June 30, 1962, for making quantitative and qualitative analyses
of the hydrologic budget and for determining the significance of
the hydrology of the Green Swamp area with respect to central
Florida.
Extremely high and unusually low annual rainfalls were
recorded during the period of investigation. The factors of the
water budget for each of the 3 complete years of record, 1959-1961,
show that average rainfall on the area ranged from 70.9 to 34.7
inches; surface runoff ranged from 31.1 to 2.3 inches; ground-water
outflow ranged from 1.8 to 2.2 inches; and water derived from
change in storage ranged from insignificant amounts in 1959 and
1960 to about 4.3 inches in 1961. Evapotranspiration losses, which
were the residuals in the water-budget equation, ranged from 39.1

FLORIDA GEOLOGICAL SURVEY

to 34.5 inches. Surface runoff varied through a wide range from
wet to dry years, while ground-water outflow varied little. The
data show that the annual losses by evapotranspiration varied
little from wet to dry years. Evaporation losses from Lake Helene
amounted to 53.1 inches during 1962.
Comparison of water-budget factors for the eastern and western
parts of the area shows that higher rates of ground-water recharge
to the Floridan aquifer occur in the eastern part.
The amount of annual runoff from the total area has not
significantly changed in recent years. However, the distribution
of the runoff has been changed by drainage canals that divert
some of the flow from the upper Oklawaha River into the
Withlacoochee River.
Impoundment of water in Green Swamp would provide some
flood protection for the lower Hillsborough River and the lower
Withlacoochee River basins. Impoundment of the total discharge
from Green Swamp to the Hillsborough River during the March
1960 flood would have reduced the flood crest at 22nd Street, Tampa,
by about 1 foot. Impoundment of the March 1960 flood discharge
in reservoirs proposed for the Green Swamp area (Corps of
Engineers, 1961) would have reduced the flood crest of the
Withlacoochee River at the Trilby gaging station by about 4 feet
and at the Croom gaging station by about 1.7 feet.
Impoundment of water in Green Swamp Reservoir would have
little effect on ground-water outflow from the total Green Swamp
area because of increased seepage rates beneath the levee, increased
evaporation losses, and because the aquifer under present conditions
is essentially full. Impoundment of water in the Southeastern
Conservation Area (Johnson, 1961) would increase the seepage
rates during dry periods by about 60 percent. Impoundment of
water will become more significant relative to ground-water
recharge as pumpage from the Floridan aquifer increases.
High piezometric levels in the southeastern part of the Green
Swamp area are caused partly by a relatively slow rate of
ground-water outflow due to sand-filled fractures, caverns, and
sinkholes in the Floridan aquifer.
Mineral content and calcium carbonate saturation studies show
that generally the water in the Floridan aquifer in central Florida
is low in mineral content and undersaturated.
Interpretation of quantitative and qualitative data indicate
that recharge to the Floridan aquifer in the Green Swamp area is
about the same as that in other parts of central Florida.

REPORT OF INVESTIGATIONS NO. 42

INTRODUCTION

To satisfy the demands of a rapidly increasing population, many
acres of land in Florida are converted each year to residential and
industrial uses. Urbanization of these areas and the demand for
increasing the food supply thus require that man search for new
areas to develop for agricultural uses. This search, in many
instances, has led to the development of marginal lands.
The Green Swamp area, shown in figure 1, in central Florida
is an area where man is developing agricultural land from marginal
land. The present efforts for its development are similar to the
early efforts for developing the Everglades in that many miles of
canals and ditches have been constructed to improve the drainage.

.Figure 1. Map of Florida showing location of Green Swamp area.

FLORIDA GEOLOGICAL SURVEY

PURPOSE AND SCOPE

Lest the early mistakes of the Everglades be repeated, the
Florida Division of Water Resources and Conservation considered
that an appraisal of the physical and hydrologic features of the
Green Swamp area was needed for future guidance in planning
water-resource policy. Lack of factual hydrologic information has
contributed to the controversy on whether the area should be
utilized for flood control and water conservation or for agriculture.
This investigation provides factual information on the hydrology
of the area for determining the feasibility of either choice of
utilization.
The hydrology of the Green Swamp area was investigated by
the U. S. Geological Survey in cooperation with the Florida
Geological Survey, the Florida Division of Water Resources and
Conservation, and the Southwest Florida Water Management
District. The investigation covered a 4-year period beginning July
1, 1958. A Comprehensive Report on Four River Basins, Florida,
was prepared by the Corps of Engineers in 1961.
The following factual data, used to appraise the hydrologic
significance of the area, were collected during the investigation;
the amount of rainfall on the area; the pattern of surface-water
drainage; the effects of improved drainage channels and man-made
diversions; the amount and direction of surface-water runoff; the
amount and direction of ground-water outflow; the amount of
evaporation losses from an open water surface; the interrelationship
of rainfall, surface water, and ground water; and the chemical and
physical characteristics of water in relation to the hydrologic
environment.
A comprehensive appraisal of the hydrology of the Green
Swamp area and its significance to central Florida have been made
on the basis of the findings of this investigation. The report does
not recommend any plan of development or utilization of the water
resources of the area. An appraisal was made, however, of the
hydrologic effectiveness of a plan of water control and water
conservation proposed by the U. S. Corps of Engineers (1961).

PREVIOUS INVESTIGATIONS

Only cursory investigations of the water resources and geology
of the Green Swamp area were made prior to this investigation.
Few long-term records of streamflow, ground-water levels, and

REPORT OF INVESTIGATIONS NO. 42

chemical quality had been collected in the vicinity as part of the
statewide data-collection programs.
Many of the physical and hydrologic features of the area are
given in an interim report by Pride, Meyer, and Cherry (1961).
General descriptions of the geology of the region have been
given by Cooke (1945), Vernon (1951), White (1958), and Stewart
(1959). Stringfield (1936) defined and described the principal
artesian aquifer of Florida.
Analyses of water from surface and ground sources in the
vicinity of the Green Swamp area are given in reports by Collins
and Howard (1928) and Black and Brown (1951).

METHODS OF INVESTIGATION

Most of the data for the investigation were collected during
the 4-year period from July 1958 to June 1962 and covered a wide
range of hydrologic conditions.
The investigation of the water resources of the Green Swamp
area involves studies of water in three main physical environments:
(1) precipitation, which occurs as rainfall; (2) surface water, which
occurs on the surface of the ground; and (3) ground water, which
occurs beneath the surface of the ground.
Waters in these environments are interrelated. Thus, it was
necessary to study the whole process or system, rather than any
part, to understand and to evaluate the water resources of the area.
The methods of studying water in each environment are
different. Some characteristics of water in the three environments
may be measured directly; some may be evaluated by analysis of
representative samples from which results may be inferred; and
some characteristics and quantities must be determined indirectly.
For instance, the chemical characteristics of the water at a
particular place can be used as an indication of the environment
through which the water has passed. The surface materials in the
Green Swamp area are relatively insoluble and the surface waters
are therefore low in mineral content. The rock below the surface
materials is relatively soluble and the contained water is
considerably more mineralized. Mineralized streamflow in areas
such as the Green Swamp, where industrial and municipal disposals
into streams are minor, indicates ground-water inflow into streams.
Therefore, the chemistry of the water can be used as a tool to give
a more complete evaluation of the hydrology of the area.

FLORIDA GEOLOGICAL SURVEY

Daily records of rainfall were collected at 24 stations located as
shown in the figures on pages 2 and 5. Some of these records
are from U. S. Weather Bureau long-term stations. Short-term
rainfall records were collected at stream or well data-collection
stations during part of the investigation using standard 8-inch
gages with tipping-bucket attachments to the water-stage
recorders.
Surface-water characteristics of the area were determined by
collecting stage, streamflow, and chemical-quality data at gaging
stations and at miscellaneous sites; by making field and aerial
reconnaissance of the area; and by studying maps and aerial
photographs.
All surface-water data-collection stations are presented in table
1 and located in figure 2 and in the figure on page 5. The grid
coordinate number shown in column 2 of table 1 is based on the

well-numbering system shown in figure 3. Records of streamflow
and stage at 24 sites and of stage of 20 lakes were collected in or
near the area of investigation.

Information on the quality of surface water was obtained during
high, intermediate, and low flows to determine the general chemical

characteristics and the extremes in quality characteristics during
the period of study. These data were supplemented with a series of
reconnaissances over the entire area generally within a period of

REPORT OF INVESTIGATIONS NO. 42

1 to 3 days. The data were used to determine the quality of water
prevalent in the area at a given time and to help determine the
interrelations between surface water and ground water.
Ground-water characteristics were determined by collecting
data concerning water levels, surface and subsurface geology, and
water chemistry from an inventory of existing wells in the Green
Swamp area and vicinity (fig. 2). Information on the depth of the
well, the amount of casing, and the depth to static water level was
recorded for more than 600 wells. Most of the inventoried wells
penetrated the Floridan aquifer. The approximate elevation of land
surface above mean sea level was determined at each well by use
of either altimeter, topographic maps, or spirit level. These data
were supplemented by selected data collected prior to this
investigation and by test drilling to provide better coverage of
the area.
The well-numbering system that is derived from latitude and
longitude coordinates is based on a state-wide grid of 1-minute
parallels of latitude and 1-minute meridians of longitude, shown in
figure 3.
Instruments were used to record continuously the water-level
fluctuations in the various aquifers. These data were supplemented
by periodic determinations of water levels and chemical character-
istics of water in selected wells in order to evaluate areas of
recharge and discharge for the aquifers.
The wells in which continuous and selected periodic water-level
data, and quality-of-water data were collected, are presented in
table 2.
During the periods October to December 1959 and May to June
1962, water-level measurements were made to prepare piezometric
maps which show the direction of water movement in the Floridan
aquifer. Hydraulic gradients scaled from these maps were used to
infer rates of water movement.
To obtain general information on the occurrence of artesian
and nonartesian ground water in the Green Swamp area, 26 test
wells were drilled at 16 different sites. At 9 of these sites a pair
of wells were drilled (one into the Floridan aquifer and one into
the nonartesian aquifer). A summary of test-well data is presented
in table 3. During the drilling, samples of rock cuttings were
collected. The lithology of the various formations and significant
changes in water levels were recordered in the well log.
Examination of rock cuttings of selected wells were supplemented

May 1958 to May 1962
November 1956 to May 1962
August 1955 to February 1960
February 1960 to June 1962

March 1956 to February 1960
February 1960 to June 1962
November 1959

February 1956 to February 1960
February 1960 to June 1962
March 1962
November 1959

July 1954 to February 1960
August 1955 to June 1962
January 1956 to June 1962
November 1959

February 1962
February 1962
February 1962
January 1958 to May 1962
November 1959
June 1955 to March 1956
March 1956 to June 1962
November 1959

June 1955 to June 1962
February 1962
February 1962
1946 to June 1962

Sp
A(1)

Sp
A ()
A(1)

Sp
Sp
Sr
Sp
Sr
Sp
A(1)
Sr
Sp
A(1)
A(1)

Sp
Sp
Sp
A(1)
A(1)
A(1)
A(1)

Sp
A(1)

Sp
Sr
A(1)
Sp
A(1)
A(1)

I

REPORT OF INVESTIGATIONS No. 42 13

TABLE 2. (Continued)

Type and
frequency
Well number County Aquifer of record Period of record

810-136-2 Po N Sr 1948 to June 1962
(P-47)
810-144-1 Po F Sp July 1959 to October 1960
Sr October 1960 to June 1962
A(21), July 1959 to April 1962
K(5),
T(4),
B(4)

810-144-2 Po N Sr October 1960 to June 1962
A(3), July 1959 to November 1961
K(2)

810-149-1 Po F A(2) November 1959 to March 1962
810-149-2 Po F Sp January 1955 to May 1962
810-151-2 Po F Sp February 1960 to May 1962
810-207-1 Pa F Sp June 1960 to May 1962
813-147-1 Po F A(1) February 1962
813-149-1 Po F Sr March 1959 to June 1962
A(6) April 1959 to March 1962

813-149-2 Po N Sr April 1959 to June 1962
813-150-2 Po N Sr October 1960 to June 1962
813-201-1 Po F Sp August 1959 to June 1962
A(2) November 1959 to March 1962

814-143-1 Po F Sr October 1960 to June 1962
814-143-2 Po N Sr October 1960 to June 1962
814-148-1 Po F Sp October 1955 to July 1957
Sr July 1957 to April 1959

814-210-1 Pa F A(1) March 1962
814-210-2 Pa F A(1) March 1962
815-134-1 Po F Sp August 1960 to October 1960
Sr October 1960 to June 1962
A(1) March 1962

815-134-2 Po N Sp August 1960 to October 1960
Sr October 1960 to June 1962

815-139-1 Po F A(1) June 1959
815-139-2 Po F Sp August 1960 to October 1960
Sr October 1960 to June 1962

815-139-3 Po N Sr October 1960 to June 1962
815-149-3 Po F Sp July 1960 to November 1960
Sr November 1960 to June 1962
A(1) April 1961
815-157-2 Po F Sp March 1956 to May 1958
Sr May 1958 to June 1962
A (1) November 1959
815-203-1 Po F A(1) February 1962
816-202-1 Po F A(2) May 1951 to-March 1962
816-202-2 Po F A(1) May 1961

14 FLORIDA GEOLOGICAL SURVEY

TABLE 2. (Continued)

Type and
frequency
Well number County Aquifer of record Period of record

816-206-1 Pa F Sp July 1959 to June 1962
A(2) November 1959 to March 1962
816-211-1 Pa F Sp 1936 to August 1951
Sr August 1951 to March 1962

849-147-1 Po F A (1) November 1959
819-151-1 Po F Sp October 1955 to June 1962
819-211-2 Pa F Sp December 1959 to June 1962
821-158-2 Su F Sp October 1959 to June 1962
821-202-1 Su F A(1) May 1959
821-202-3 Su F Sr March 1959 to June 1962
A(2) May 1959 to November 1959

822-138-2 Or N Sr April 1959 to June 1962
822-149-1 La F Sr February 1959 to March 1962
A (8) April 1959 to March 1962
822-149-2 La N Sr April 1959 to June 1962
822-149-3 La F A(1) February 1962
822-210-1 Pa F Sp October 1959 to June 1962
822-211-1 Pa F A(1) February 1959
824-142-1 La F Sp December 1959 to June 1962
824-206-1 Pa F Sp November 1958 to June 1962
824-211-1 Pa F Sp December 1959 to June 1962
824-211-2 Pa F A (1) February 1962
825-151-1 La F Sp Ocober 1959 to June 1962
826-208-1 Pa F Sp November 1958 to June 1962
826-211-1 Pa F Sp October 1959 to February 1960
Sr February 1960 to June 1962

REPORT OF INVESTIGATIONS NO. 42 15

TABLE 2. (Continued)

Type and
frequency
Well number County Aquifer of record Period of record

827-144-1 La F A(1) February 1962
827-149-1 Po N A(1) February 1962
827-154-1 La N A(1) February 1962
827-158-1 Su F Sp July 1959 to June 1962
A(1) July 1959
827-210-1 Pa F Sp 1936-50 (U.S. Corps of Engineers)
Sp October 1959.to July 1961
827-210-2 Pa F Sp August 1961 to June 1962
828-154-1 La F Sp November 1959 to June 1962
828-203-1 He F A(2) July 1959 to November 1959
828-204-1 Pa N A(1) February 1962
828-209-1 Pa F A(1) February 1962
829-146-2 La F Sp October 1959 to June 1962
829-202-1 Su F Sp December 1959 to June 1962
829-206-1 He F Sp May 1959 to June 1962
A(3) May 1959 to November 1959
830-157-1 Su F Sp May 1959 to June 1962
A (3) May 1959 to November 1959
820-210-2 He F A(1) November 1959
832-154-1 La F Sr February 1959 to June 1962
A(9) April 1959 to March 1962
832-154-2 La N Sr February 1959 to June 1962
832-154-3 La N A(3) May 1959 to November 1959
832-204-1 Su F A (1) February 1962
833-137-2 Or F Sr March 1960 to June 1962
833-144-1 La F Sp November 1959 to June 1962
833-144-2 La F A(1) March 1962
833-151-1 La F Sp November 1959 to June 1962
833-151-5 La F A(1) March 1962
833-209-1 He F A(1) February 1962
834-159-1 Su F Sp November 1959 to June 1962
836-202-1 Su F A (1) March 1962
836-202-2 Su F A(1) February 1962
836-208-2 Su F A (1) February 1962
838-159-2 Su F A (1) November 1959
841-156-1 La F Sp March 1961 to June 1962

by interpretation of electric and gamma-ray logs of some wells and
geologists' and drillers' logs of wells which are on file with the
Florida Geological Survey.

GEOGRAPHY

One of the most prominent topographic features in the central
part of the Florida Peninsula is Green Swamp which is an
extensive area of flatland and swampland at a relatively high
elevation. Five major drainage systems originate in or near the
Green Swamp area and flow in several directions to the sea. The
area contains the headwaters of the Oklawaha River, which flows
generally northward to become the largest tributary of the St.
Johns River; the Kissimmee and Peace Rivers that flow southward;
the Hillsborough River that flows southwestward; and the Withla-
coochee River that flows northwestward.

LOCATION

The Green Swamp area is in central Florida (see fig. 1) west
of and adjacent to a high sandy ridge that forms the major axis
of the peninsula. For this study the boundaries of the area were
established arbitrarily and the Green Swamp area should not be
confused with a small drainage basin that is generally known as
Green Swamp Run in the headwaters of the Big Creek watershed
in southern Lake County and northeastern Polk County. The
boundaries of the Green Swamp area, as designated for this
investigation, have been extended to encompass a much larger
area. The project area includes the southern parts of Lake and
Sumter counties, the northern part of Polk County, and the
eastern parts of Pasco and Hernando counties (see fig. 2).
The eastern boundary of the Green Swamp area is U. S.
Highway 27, from Clermont south-southeastward to Haines City.
The southern and southwestern boundaries of the area generally
coincide with the divides separating drainage northward to the
Big Creek and Withlacoochee River basins from drainage south-
ward to the Peace and Hillsborough River basins. These boundaries
follow a meandering line westward from Haines City to a point
two miles north of Lakeland and then northwestward to Dade City.
The western boundary of the area is U. S. Highway 301 northward
from Dade City to St. Catherine. The northern boundary extends
from St. Catherine eastward along the Little Withlacoochee River

FLORIDA GEOLOGICAL SURVEY

basin divide to State Highway 50 and along State Highway 50
eastward to Clermont. The boundaries described enclose an area
of 870 square miles.

TOPOGRAPHY

The Green Swamp area is in the Central Highlands topographic
region as defined by Cooke (1945). The area is bordered on the
eastern side by the Lake Wales Ridge, on the southern side by the
northern termini of the Winter Haven and Lakeland Ridges, and
on the western side by the Brooksville Ridge (White, 1958, pp.
9-11). Figure 4 shows the locations of these ridges.
Although the area is designated the Green Swamp, it is not a
continuous expanse of swamp but is a composite of many swamps
that are distributed fairly uniformly within the area. Interspersed
among the swamps are low ridges, hills, and flatlands. Several
large and many small lakes of sinkhole origin rim the southeastern
and northeastern parts of the area. The elevation of the land
surface ranges from about 200 feet above mean sea level (msl)
in the eastern part to about 75 feet in the river valleys in the
western part.
Prominent topographic features affecting the drainage of the
eastern part of the area are the alternating low ridges and swales
that trend generally north-northwestward from the southern
boundary to the Polk-Lake County line. The ridges parallel the
major axis of the Florida Peninsula and their configuration suggests
that they were formed by subsidence and erosion along fractures
and joints. Aerial photographs of the area between U. S. Highway
27 and the Seaboard Air Line Railroad show five of these long
narrow ridges with intervening swales.
In the western part of the Green Swamp area there is little
evidence of the elongated ridges, and the main land-surface features
are large swamps, flatlands, and rolling hills. There are many
small swamps in patches and strips generally less than half a mile
wide. Most of these swamps support good growths of cypress
trees while in the uplands pine and scrub oak trees grow
abundantly. The largest continuous. expanse of swampland lies
within the valley of the Withlacoochee River and is more than a
mile wide at places. Limestone is exposed in the western part of
the Green Swamp area.

REPORT OF INVESTIGATIONS NO. 42

DRAINAGE

The drainage system of the Green Swamp area and vicinity is
shown on the map in figure 5. The headwaters of four stream
systems within the Green Swamp area, listed in order of their
proportion of the area drained, are: Withlacoochee River, Little
Withlacoochee River, Oklawaha River, and Hillsborough River.
Other streams that head near the boundaries of the Green Swamp
area are: Reedy, Davenport, and Horse creeks in the Kissimmee
River basin; Peace Creek drainage canal and Saddle Creek in the
Peace River basin; Fox Branch in the Hillsborough River basin;
and Jumper Creek Canal and a major canal that head northwest
of Mascotte in the Withlacoochee River basin. Of the total area
of 870 square miles, 710 square miles are drained by the
Withlacoochee River and its tributaries.
The surface drainage of the Green Swamp area is poor because
of the flat topography and lack of well developed stream channels.
Following heavy rainfall, water stands in large shallow sheets over
much of the area.
Boundaries of the elongated north-south drainage basins, in
the eastern part of the Green Swamp area, are formed by low
ridges. The valleys between the ridges are not deeply incised but
their effectiveness as drainage channels has been improved by
many miles of canals and ditches. Some parallel drainage basins
are interconnected in several places by gaps or saddles through
the ridges. Through these gaps water may flow at times from one
stream valley into another. The amount and direction of flow
depend on the relative elevation of water levels in the adjoining
basins and the hydraulic conveyance of the connecting channels.
The canals and ditches, for the most part, have been dug to
follow the natural drainage courses through the shallow swamps.
However, in some places, probably to provide firm footing for the
excavation equipment and to avoid clearing through the dense
growth of cypress trees, the ditches have been dug along the edges
of the large swamps rather than through the interior. Also, to
provide better alignment in some places, the ditches have been cut
through ridges to connect the adjacent swamps. These shortcuts
have bypassed the circuitous natural drainage routes and have
straightened and shortened the courses of the waterways.
Surface drainage from most of the Green Swamp area is
generally toward the north and west. However, the headwaters of
the Peace River basin originate along the southern boundaries of

FLORIDA GEOLOGICAL SURVEY

the area and the flow is generally southward. Along the eastern
boundary of the area, drainage is toward the east and southeast
into the Kissimmee River basin. Other drainage from the Green
Swamp area is toward the southwest into the Hillsborough River
via a natural channel in eastern Pasco County.
The subsurface drainage of the Green Swamp area is generally
poor. Ground-water levels in the interior of the area remain near
the surface most of the time, consequently the aquifers provide
little opportunity to store water from heavy rainfall. Ground-water
levels fluctuate through a greater range in the ridges that form the
eastern, southern, and western boundaries. The wide range of
fluctuation indicates better subsurface drainage and greater storage
capacity along the boundaries than in the interior.
Subsurface drainage is through both the Floridan and the
nonartesian aquifers but most is via the Floridan aquifer. Water
percolates downward from the overlying nonartesian aquifer to the
Floridan aquifer or enters exposed portions of the Floridan aquifer.
Movement of ground water in the Floridan aquifer is generally
outward in all directions from the southeastern part of the area.
However, the areas contributing to the aquifer (p. 80) show that
the predominant directions of ground-water movement are east and
west. The ground-water divides in the aquifer shift slightly in
response to demands in each contributing area. Most of the surface
area that potentially would contribute recharge to the Floridan
aquifer in Green Swamp lies within the Withlacoochee River basin.
The distribution of ground-water outflow originating in each
surface basin is shown in the tables on pages 116 and 117.

CULTURE AND DEVELOPMENT

The Green Swamp area is sparsely populated except for a few
small towns and communities on the ridges along the border and
along State Highway 33.
Most of the land is in large tracts owned by private individuals
or corporations. The only large tract of public land in the area is
the Withlacoochee State Forest, part of which is within the
boundaries of the Green Swamp area in Sumter, Hernando, and
Pasco counties.
The principal industry is agriculture. Much of the upland area
has been cleared and planted in citrus groves. Other upland areas
have been cleared and are used for cattle raising. Very little of
the land is cultivated. The low swampland is unsuitable for

REPORT OF INVESTIGATIONS NO. 42

agriculture because of poor drainage. In spite of the many miles of
ditches, drainage is still inadequate. Even in the cleared areas that
are suitable for agriculture, few attempts have been made to
reclaim the many small, round, cypress swamps that dot the area.
Cypress lumbering was once an important industry in the
western part of the area, particularly in the Withlacoochee River
Swamp where there were extensive stands of trees. The first access
roads to penetrate the interior of the swamp were trails and tram
roads built for cypress lumbering. Timber and pulpwood are now
produced from the pine flatwoods interspersed among the swamps.
There is some development of the mineral resources of the area
for the commercial market. Extensive phosphate deposits in Polk
County lie just south of the Green Swamp area. Some phosphate
is mined within the area but the amount is only a small percentage
of that produced in southern Polk and eastern Hillsborough
counties. Limerock, used in road construction and agriculture, is
mined in the northwestern part of the area. Deposits of sand,
suitable for building uses, are mined in many places in the eastern
part of the area.

CLIMATE

The location of the Green Swamp area, well south in the
Temperate Zone, and its proximity to large bodies of warm water
produce a warm humid climate. Precipitation and temperature, the
principal climatic elements that influence the hydrology of the
Green Swamp area, are described separately.

PRECIPITATION

The study of precipitation in central Florida can be restricted
to rainfall only, because snow and hail are virtually unknown. The
normal or long-term average annual rainfall of the Green Swamp
area is 52.7 inches. This normal is computed by the Thiessen
method of weighting long-term rainfall records at each of the
following U. S. Weather Bureau stations in or near the project area:
Clermont 6 miles south, Lake Alfred Experiment Station, Lakeland,
and St. Leo (figs. 2 and 5).
The average rainfall for the station at St. Leo, west of the area,
is slightly higher than that for the other three stations which are
located farther inland. The average rainfall at the four stations
ranges from a minimum of 50.1 inches at the Clermont station to

FLORIDA GEOLOGICAL SURVEY

a maximum of 56.4 inches at the St. Leo station. In view of the
small deviation of these extreme values from the mean, the
weighted average rainfall of 52.7 inches for the area of
investigation appears to be reasonably accurate.
The amount of rainfall on the area varies seasonally. About
60 percent of the annual total rainfall occurs during the wet season
from June through September. In the spring and early summer,
local thunderstorms of high intensity and short duration sweep
over the area. Showers occur almost daily, or perhaps several times
a day, during June and July. Heavier and more prolonged rainfalls
occur generally in August and September and are often intensified
by tropical storms that occasionally reach hurricane proportions.
On the other hand, there are periods of a month or more with little
or no rainfall. Periods of below average rainfall usually occur
during the winter season from November to February.
During wet years the annual rainfall is about twice that of dry
years. The annual and the mean monthly rainfalls for the years
1931-1961 are shown by bar graphs in figure 6. The maximum
annual rainfall during this 31-year period was 70.9 inches in 1959
and the minimum was 34.7 inches in 1961. Both occurred during the
period of the investigation. It is a fortunate circumstance that the
full range of hydrologic conditions was experienced during the
investigation.

TEMPERATURE

A knowledge of temperature variations in central Florida is
pertinent to a study of its water resources because of the dominant
influence of temperature on rates of water losses by evaporation
and transpiration.
The mean monthly temperature in the Green Swamp area ranges
from 610 F. for January to 82' F. for August. The lowest
temperature recorded during the 69-year period of record at the
Clermont station was 180 F. and the highest was 104 F. Daily
temperatures recorded at the U. S. Weather Bureau stations show
that all parts of the area have essentially the same temperature,
ranging no more than 2 to 30 F.
Killing frosts occur infrequently in this area, and damage to
vegetation, although severe from the standpoint of agriculture,
seldom is great enough to affect the hydrologic factors pertinent
to water supplies.

REPORT OF INVESTIGATIONS NO. 42

- in 0 0 in
rC L EN D ARn YEA
CALENDAR YEAR

Rainfall of Green Swamp area
computed from U. S. Weather
Bureau records at four stations,
weighted by Thiessen method
as follows:

Water loss from a drainage basin is the difference between the
average rainfall over the basin and the runoff from the basin for a
given period (Williams, 1940, p. 3). In humid regions, where there
is sufficient water to satisfy the demands of vegetation, the mean
annual water loss is principally a function of temperature
(Langbein, 1949, p. 7). The relation between mean annual

8

-

3

FLORIDA GEOLOGICAL SURVEY

temperature and mean annual water loss under such conditions
is shown in figure 7, which is taken from U. S. Geological Survey
Circular 52. For the Green Swamp area where the mean annual
temperature is 72' F., the annual water loss would be 48 inches
according to this figure.

ENVIRONMENTAL FACTORS AFFECTING THE
QUALITY OF WATER

The quality of water in the Green Swamp area reflects the
solubility of the material which the water contacts and its biologic
environment, both of which are natural influences. Surface water
is usually lower in mineral content than ground water because of
low solubility of materials on the surface of the ground and short
time of contact of water with the materials.
The quality of the surface water (lakes, streams, and swamps)
depends mostly on the composition of the precipitation and the

10 20

30 40

50 EO

Natural water loss, in inches
Figure 7. Relation of annual water loss to temperature in humid areas.

80

70

0 60

0.

30
E

50

4 40

30

Polatlakaho Creek above Mascotte

Withlacoochee River at Trilby-oo

SComputed annual water loss
at two gaging stations in
Green Swamp area.

(After Longbein, W. B., and
others, 1949)
_____ -_____ I I

REPORT OF INVESTIGATIONS NO. 42

biologic environment. Generally, the mineral content of water in
streams varies inversely with discharge. Surface waters are
usually highly colored and acidic. Sodium and chloride, although
in very low concentrations, are the principal dissolved mineral
constituents and may be present as a result of wind and rain-borne
salts from the ocean.
The quality of ground water in the Green Swamp area generally
meets the requirements for most municipal, industrial, domestic,
and agricultural uses. Ground water of lowest mineral content
occurs along the eastern and western boundaries of the area and
is lowest near the lakes. Ground water of highest mineral content
occurs in the central part of the Green Swamp. The principal
dissolved mineral constituents are calcium and bicarbonate which
are products of limestone solution. Relatively high concentrations
of calcium in the water cause hardness which is probably the most
objectionable characteristic of the ground water in the Green
Swamp area.

GEOLOGY'

Topographically, the surface of the Green Swamp area
resembles a basin, or trough, opening to the north. However,
geologically, the Green Swamp is part of an eroded, faulted
anticline. The oldest formations are exposed along the axis of the
anticline and eroded remnants of younger formations rim the flanks
and present a basin-like feature.
The Green Swamp area is underlain by several hundred feet of
limestone and dolomite that have been periodically exposed to
solution-weathering and erosion. The surface is mantled with a
varying thickness of plastic material (sand and clay) that was
deposited in fluctuating shallow seas. No attempt has been made
to differentiate the formations within the plastic material because
of its complexity and the lack of data.
The upper part of the elastic sediments, composed of clayey
sands, forms a distinct hydrologic unit, commonly referred to as
the nonartesian aquifer. The basal portion of the plastic sediments,
composed mostly of clay and some interbedded limestone
(secondary artesian aquifer), is less permeable than the overlying,

1The classification and nomenclature of the rock units conform to the usage
of the Florida Geological Survey and also with those of the U. S. Geological
Survey, except for the Fort Preston Formation (?), the Tampa Formation,
and the Ocala Group and its subdivisions.

FLORIDA GEOLOGICAL SURVEY

clayey sands or the underlying porous limestone. The solution-
riddled limestone formations, which underlie the clay deposits,
comprise the Floridan aquifer, the principal source of artesian
ground water in the State. Where present, the clay forms an
aquiclude which retards the rate of water movement between the
aquifers.
The principal artesian aquifer was first described by Stringfield
(1936) and later named the Floridan aquifer by Parker (1955).
According to Parker, the Floridan aquifer includes those limestone
formations ranging in age from the middle Eocene (Lake City
Limestone) to perhaps early and middle Miocene (Hawthorn
Formation). In the Green Swamp area the following formations
comprise the Floridan aquifer (from youngest to oldest); the
Suwanee Limestone; the Ocala Group which includes the Crystal
River, Williston, and Inglis Formations; and the Avon Park
Limestone. The base of the aquifer is considered to be near the
base of the Avon Park limestone at the first occurrence of gypsum
because the presence of gypsum probably indicates poor circulation
of ground water.

FORMATIONS

The formations that underlie the Green Swamp area are
presented in table 4. Generalized geologic cross sections, shown in
figure 8 were prepared based on data from wells located along lines
A-A', B-B' and C-C'.

UNDIFFERENTIATED CLASTIC DEPOSITS

Undifferentiated plastic deposits, ranging from late Miocene to
Recent in age, underlie the Green Swamp area except in the western
part where Tertiary limestones are exposed at the surface. The
deposits consist primarily of clayey sand or sandy clay. The
following lithologic sequence (from youngest to oldest) is indicated:
(1) fine quartz sand surficiall sand) with varying amounts of clay
and organic material; (2) variegated (red-orange-tan) fine to
coarse quartz sand with little clay; (3) white fine to very coarse
quartz sand with varying amounts of white-green kaolinitic or
montmorillonitic clay; and (4) white silty quartz sand with varying
amounts of mica flakes.
Generally, the deposits range from 100 to 200 feet in thickness
beneath the ridges that rim the Green Swamp area; however, they
are thin or absent in the western part and tend to become more

TABLE 4. Geologic formations and their water-bearing characteristics in Green Swamp area and vicinity.

System Series

Recent
Quaternary

Pliocene

Pleistocene

Tertiary

Miocene

Upper

Middle

Lower

Oligocene

Upper

Eocene

Middle

Formation
(after F.G.S.)

Recent
Deposits

Terrace
Sands

Citronelle
Formation

Fort Preston
Formation (7)

Hawthorn
Formation

Tampa
Formation

Suwannee
Limestone

Crystal
River
p Formation
E
0 Williston
g Formation

S Inglis
Formation

Avon Park
Limestone

Formations
used in this
report

Undifferentiated
S Clastic
Deposits

Undifferentiated
Clay

Suwannee
Limestone

Crystal River
Formation

Williston
Formation

Inglis
Formation

Avon Park
Limestone

Approximate
range of
thickness
(feet)

Lithology

Aquifer

I II i

0-200

0- 60

Light-colored clayey
sands grading Non-
into sandy clays artesian

Dark-colored phos.
phatic clay with
limestone lenses

Secondary
artesian

___________________ I I-********~~**-*

0- 80

0-120

0- 40

0- 50

800-1,000

Hard, white-yellow
limestone

Soft, gray,
limestone

Hard, tan
limestone

Hard, tan
limestone

Soft to hard,
white-brown,
dolomitic lime-
stone

Floridan

Water-bearing
characteristics

Generally poor source in the cen-
tral part of the area. A fair
source in the ridge areas.

Generally very poor except in
the Lakeland area where iriter-
bedded limestone are a fair
source.

Generally good to excellent. The
best source is the dolomitic
Avon Park Limestone. Evapo-
rite (selenite) deposits near
the base of the Avon Park
Limestone is considered to be
the base of the aquifer.

O

UI
1-I

z

z

IS

-~------I I

FLORIDA GEOLOGICAL SURVEY

clayey where they thin over the crest of the anticline (fig. 8, A-A').
The deposits appear to increase in coarseness from the interior of
the Green Swamp area eastward to the Lake Wales Ridge. Much
of these deposits occur as cavity fill in the underlying limestones
especially in the ridge areas.
The undifferentiated plastic deposits form the nonartesian
aquifer in the area. Generally, the deposits in the western part
of the Green Swamp area are thin or absent, low in permeability
and porosity; and therefore, they are of minor significance as an
aquifer.

UNDIFFERENTIATED CLAY

Undifferentiated clays of Miocene age underlie most of the area,
except in the western part, and contain varying amounts of quartz,
phosphatic sand, and interbedded limestone. The following
general lithologic sequence (from younger to older) is indicated:
(1) light gray-tan-blue-green, montmorillonitic clay with varying
amounts of quartz, phosphatic sand, and interbedded limestone;
(2) dark gray-green-blue phosphatic, silty clay with varying
amounts of quartz pebbles, silt and mica flakes.
The light-colored clay with interbedded limestone is part of the
Hawthorn Formation of early and middle Miocene age. Generally,
its occurrence is limited to the southeastern part of the Green
Swamp area. It thickens eastward and southward and forms a
secondary artesian aquifer which is a significant source of artesian
water outside of the Green Swamp area. The dark, silty clay is
probably equivalent to the Tampa Formation of early Miocene age
(Carr, 1959). Generally, its occurrence is limited to the eastern
part of the Green Swamp area where it forms an aquiclude.

SUWANNEE LIMESTONE

The Suwannee Limestone (Cooke and Mansfield, 1936) of
Oligocene age is a white dense fossiliferous limestone. It is present
in the southern and western parts of the Green Swamp area and
crops out along the Withlacoochee River near Polk-Sumter-Pasco
County line. The formation thickens southward in Polk and
Hillsborough counties and westward in Pasco County. Many of the
springs along the upper Hillsborough River flow from exposures
of Suwannee Limestone. The Suwannee Limestone overlies the
Crystal River Formation and it is overlain by either undifferen-
tiated clay or undifferentiated plastic deposits.

REPORT OF INVESTIGATIONS NO. 42

OCALA GROUP

The Ocala Group (Puri, 1957) includes three limestone
formations of late Eocene age. The subdivisions of the Ocala Group
(from youngest to oldest) are the Crystal River, the Williston,
and the Inglis Formations.

CRYSTAL RIVER FORMATION

The Crystal River Formation is primarily a coquina of large
foraminifers and crops out in an area extending from northern
Polk County through the southern end of Sumter County and into
eastern Hernando County. It ranges from 50 to 120 feet in
thickness, except in the eastern part of the area where it is absent.
In the central part of the area, the formation contains many
sand-filled cavities.

WILLISTON FORMATION

The Williston Formation is a tan-cream, medium to hard
limestone containing abundant micro-fossils. The formation is
slightly coarser than the underlying Inglis Formation but generally
finer than the overlying Crystal River Formation. In most of the
area, the Williston Formation ranges from 20 to 40 feet in thickness.
It is thin or absent along the eastern boundary of the area.

INGLIS FORMATION

The Inglis Formation is generally a white-tan, hard, fossil-
iferous limestone. The texture of the formation appears to be finer
than that of the Crystal River and Williston Formations. In most
of the area, the Inglis Formation is about 50 feet thick. It is thin
or absent along the eastern boundary of the Green Swamp area.

AVON PARK LIMESTONE

The Avon Park Limestone (Applin and Applin, 1944) of late
middle Eocene age was the deepest formation penetrated by test
drilling. The formation is nearest the surface on an upthrown
fault block along the eastern side of the area (fig. 8, A-A'). The
formation is found at considerable depth in the area south and
southwest of Green Swamp. The top of the formation is

FLORIDA GEOLOGICAL SURVEY

characterized by a distinct color change from tan to brown
limestone and by abundant cone-shaped foraminifers. The formation
is a brown, dolomitic, porous limestone. Selenite (gypsum) near
the base of the formation probably forms the bottom of the
Floridan aquifer. The Avon Park Limestone is highly permeable
and is the main source of water for most of the high-capacity wells
in the area. Figure 9 shows the configuration of the top of the
Avon Park Limestone. The map shows the northwest-southwest
trend of the faulted anticline.

STRUCTURE

The Peninsular arch (Applin, 1951), a buried anticlinal structure
of Paleozoic sediments, trends generally north-northwestward and
its main axis is located east of the Green Swamp area. A flexure,
developed on the western flank of the Peninsular arch in the
Tertiary limestones, is called the Ocala Uplift. The Green Swamp
area is located at the southern end of the Ocala Uplift (figs. 8
and 9).
Vernon (1951) dated the Ocala Uplift as post-Oligocene in age.
Faults in the Green Swamp area complicate the definition of the
geology and the hydrology. The main area of faulting occurs
along the Lake Wales Ridge. Faulting in this area was described
by Vernon (1951, p. 56) and named The Kissimmee Faulted Flexure.
The cross sections in figure 8 show vertical displacement along
fault zones.
The faults are probably post-Oligocene. Subsequent movement
along fault zones may have occurred over a long period of time,
the later movements being associated primarily with subsidence
and sinkhole collapse along the solution-widened zones.
Figure 9 shows a structural map based on the top of the Avon
Park Limestone. The contour lines generally define the shape of
the anticline with associated faults. The linearity of ridges on the
anticline suggests that other faults exist in the area.
Faulting probably could affect the hydrology of the Green
Swamp in the following ways:
(1) Joints or faults within the Floridan aquifer, widened by
solution, could cause zones of high permeability, or could cause
zones of low permeability when filled with plastic materials.
(2) Displacement along the faults could position formations
of different lithology (hence permeability) one against the other,

The water supply of the earth, whether it is on the surface or
below the ground, has its origin in precipitation. Of the
precipitation that reaches the ground, part is returned to the
atmosphere by evapotranspiration; part remains above ground and
is stored temporarily in lakes, ponds, and swamps, or moves to
the sea as streamflow; and part percolates into the ground, some
to replenish the soil moisture and some to enter the zone of
saturation and recharge the ground-water aquifers. Ground water
moves in the aquifers under the influence of gravity, towards areas
of discharge such as streams, lakes, springs, wells and the oceans.

WITHLACOOCHEE RIVER BASIN

DESCRIPTION OF BASIN

TheWithlacoochee River drains 82 percent of the Green Swamp
area. The total drainage area at stations 42 and 43 at the western
boundary is 740 square miles, all of which is within the project
area except for 45 square miles of lakes and hills west of U. S.
Highway 301 and south of U. S. Highway 98 near Dade City.
Most of the general topographic and drainage features of the
Green Swamp area, described in preceding sections of this report,
apply to the Withlacoochee River basin in particular. The following
description of the basin refers specifically to this stream system.
The Withlacoochee River heads in a group of lakes and swamps
in the north-central part of Polk County in the vicinity of Polk
City and the town of Lake Alfred (see fig. 5). Lakes Van and
Juliana, the uppermost of these headwater lakes, drain into Lake
Mattie. Surface drainage from Lake Mattie spills through a wide
shallow marsh along the northeastern shoreline and flows
northward through a series of interconnected shallow swamps and
ditches to the northern boundary of Polk County. This is generally
considered to be the major headwater channel of the Withlacoochee
River. Other headwater tributaries originate in the marshes
between Lakes Mattie and Lowery and flow generally northward
between the confining ridges. These -channels join near the

FLORIDA GEOLOGICAL SURVEY

northern boundary of Polk County and flow westward to form the
Withlacoochee River.
West of State Highway 33 the tributaries of the Withlacoochee
River are not confined by the ridges that are prominent in the area
east of the highway. These tributaries have developed basins that
are generally more fan-shaped than those in the eastern part.
Pony Creek, which flows northwestward, is the first of the large
tributaries entering the Withlacoochee River west of the Seaboard
Air Line Railroad. Pony Creek heads in a swamp east of Lake
Helene near Polk City. Lake Helene has no surface outlet except
at extremely high stages when it overflows into the Pony Creek
basin.
Grass Creek, the next large tributary, empties into the
Withlacoochee River about one mile downstream from Pony Creek.
Grass Creek heads in a group of small lakes in the vicinity of Polk
City. the largest of which is Lake Agnes. The outlet from Lake
Agnes is a ditch leading from the northern end of the lake and
connecting with the network of canals and ditches that carry the
water northwestward through the swamp. Several other tributaries
flow into Grass Creek as it crosses the swamp.
Gator Creek empties into the Withlacoochee River at the
Polk-Pasco County line. This is the largest tributary upstream
from the diffluence of the Withlacoochee River to the Hillsborough
River. Gator Creek heads in several small swamps northeast of
Lakeland and flows northwestward through a network of swamp
channel and ditches.
From the point of diffluence to the Hillsborough River, the
channel of the Withlacoochee River turns abruptly to the north and
continues northwestward to the western boundary of the Green
Swamp area at U S. Highway 301.
About 14 miles downstream from the point of diffluence, a major
canal draining several lakes and swamps east of Dade City empties
into the river from the west. This canal also carries the drainage
from an area of hills and lakes west of Dade City and the effluent
from citrus concentrate plants at Dade City.
One of the larger tributaries entering the Withlacoochee River
from the east is formed by the confluence of Devils Creek and
Gator Hole Slough. Devils Creek heads in a swamp about 21/
miles east of the Sumter-Pasco County line. At high stages some
water from the Withlacoochee River moves through a gap in a low
ridge into Devils Creek. This water returns to the Withlacoochee
River farther downstream.

REPORT OF INVESTIGATIONS NO. 42

Gator Hole Slough heads just east of the Seaboard Air Line
Railroad and flows westward through an unimproved swamp
channel, entering the eastern boundary of the Withlacoochee State
Forest about 3 miles west of the railroad. It continues within the
boundaries of the Forest to its confluence with Devils Creek which
empties into the Withlacoochee River 21/ miles farther west.
The Little Withlacoochee River, the largest tributary of the
Withlacoochee River, heads near State Highway 33 in Lake County
and flows westerly. Bay Root Slough is the headwater tributary
of the Little Withlacoochee River. This stream carries the drainage
from several lakes and swamps east of the Seaboard Air Line
Railroad and flows northwestward to the Lake-Sumter County line
at the eastern boundary of the Withlacoochee State Forest. The
river channel within the Forest is wide and shallow and contains
dense growths of cypress trees. The channel has been allowed to
remain in its natural swampy condition to store as much water as
possible, rather than to remove the water by improved drainage,
as a precautionary measure against fire damages to the valuable
cypress and pine trees in the Forest. The Little Withlacoochee
River emerges from the Forest near the Sumter-Hernando County
line, where it is joined on the north by a major canal. This canal
drains a swampy area between the Forest and State Highway 50.
The river continues westward through the swamp to the crossing
of State Highway 50 where it turns and flows northwestward
toward U. S. Highway 301. Another canal joins the river about a
quarter of a mile upstream from U. S. Highway 301. This canal
heads near Webster, flows southward about 11 miles, then turns
westward to Big Gant Lake and then to the Little Withlacoochee
River. The Little Withlacoochee River continues westward and
empties into the Withlacoochee River 3 miles downstream from
U. S. Highway 301.
STREAMFLOW

Streamflow data for gaging stations in the Withlacoochee River
basin during the data-collection phase of the investigation are
summarized in table 5.
Flow-duration curves for five gaging stations in the Withla-
coochee River basin are given in figure 10. Records for only the
Trilby gaging station are continuous for the 311/2-year period,
1931-62. The curves for the other four stations in the basin have
been adjusted from their individual short-term records to the
31/-year base period.

TABal, 5, Struainflow data for Withlacoochee River basin gaging stations in Green Swamp area
(see figure 5 for station locations)

The flow-duration curves indicate the percentage of time that
specified discharges were equaled or exceeded during the period
of record. These may be considered probability curves used to
estimate the percent of time a specified discharge will be equaled
or exceeded in the future. The use of flow-duration curves to
indicate the future pattern of flow from a basin is valid only if the
climatic conditions remain the same and the amount and
distribution of runoff from the basin is not significantly changed
by man.
The flow-duration curve for Withlacoochee River at Trilby
(station 42) may be only an approximate representation of duration
of future low flows because of the progressive increases in
ground-water inflow by pumpage above the gaging station.
However, the flow-duration curves for the other four stations
shown in figure 10 may be considered probability curves and used
to estimate the percent of time that a specified discharge will be
equaled or exceeded in the future.
During a period of extremely low flow on May 23-25, 1961,
streamflow was measured and water samples for chemical analysis
were collected at several sites on the Withlacoochee River. The
results of this low-flow investigation are shown on the map in
figure 11.
The base flow of the Withlacoochee River near Dade City
(station 40) represents the natural drainage from 390 square miles
because no surface flow is diverted to the Hillsborough River basin
through the overflow channel, C-9. Since about 1941 or 1942, the
effluent from citrus processing plants at Dade City has been drained
into the Withlacoochee River by way of the Pasco Packing Company
canal. The water used by these plants is pumped from deep wells.
Measurements at station 41 of the effluent from the Pasco Packing
Company canal during 1958-62, ranged from 5 cfs, when the plant
was at minimum operation, to about 76 cfs at peak operation during
the citrus packing season. Inflow to the river from this plant and
others at Dade City produces higher discharge below station 40
east of Dade City than would be derived from the natural yield of
the basin. During dry periods, the effluent at Dade City greatly
exceeds the base flow of the Withlacoochee River (see fig. 11).
The drainage area above Trilby (station 42) comprises
two-thirds of the Green Swamp area and the record collected at this
station is a good index of the long-term variations of surface runoff
from the entire area except at low flow.

REPORT OF INVESTIGATIONS No. 42

The discharge at the Trilby gaging station does not represent
the natural runoff from the Withlacoochee River basin because of
the high-water flow diverted from the basin to the Hillsborough
River by the Withlacoochee-Hilisborough overflow channel (C-9)
and the effluent into the river from the citrus concentrate plants
at Dade City. When the Withlacoochee River reaches a stage of
about 78.5 feet above msl at the overflow channel, part of its flow
is diverted into the Hillsborough River. At high stages more than
a fourth of the flow from the upper Withlacoochee River is diverted
through this channel. Computations of basin runoff for either the
Withlacoochee or the Hillsborough Rivers must be adjusted for the
amount of discharge from one basin to the other. Percentagewise,
the plant effluent into the basin is small except when the discharge
in the Withlacoochee River is extremely low and the plant is at peak
operation.
The annual and mean monthly discharges at the Trilby gaging
station are shown by the bar graphs in figure 12. The general
relation between rainfall and streamflow is evident from figures 6
and 12. During the wet years of 1959 and 1960, annual rainfall over
the Green Swamp area was 70.9 inches and 69.5 inches, respectively.
The annual mean discharge at the Trilby gaging station was 1,157
cfs for 1959 and 1,209 cfs for 1960. The higher runoff for 1960 was
probably the result of a carry-over from the high rainfall of 1959.
The maximum discharge of record at the Trilby station was
8,840 cfs on June 21, 1934. Flood-frequency studies by Pride (1958)
indicate that the recurrence interval of a flood at this magnitude
is more than 100 years. The peak discharge of the flood of March
1960 was 6,920 cfs and was the third highest flood of record. The
recurrence interval of a flood of this magnitude is about 40 years.
The drought of 1954-56 was the most severe dry period of
record, considering its 3-year duration and yearly deficiencies.
Annual rainfall on the basin above the Trilby station for 1954-56
was 39.9, 40.2, and 46.2 inches per year, respectively. The prolonged
period of low rainfall resulted in low discharges at the Trilby
station during each of the 3 years. The lowest annual mean
discharge at the Trilby station was 75.4 cfs for 1932, a year in
which the total rainfall amounted to 39.6 inches. The total annual
rainfall on the basin in 1961 amounted to only 35.2 inches and was
the minimum for any year of record. Effluent from citrus
concentrate plants, derived from ground-water sources, accounted
for the higher annual mean discharges for 1954-56 and 1961 than
that for 1932.

The graph of mean monthly discharge for the Withlacoochee
River at Trilby (fig. 12) shows that runoff from the basin is lowest
for the months of November through June. The season of highest
runoff is the 4-month period, July through October. During these
months, 58 percent of the runoff from the basin occurs.

CHEMICAL CHARACTERISTICS OF SURFACE WATER

Waters of the Withlacoochee River in the eastern part of the
-reen Swamp area are very low in mineral content (figure 13
i, b) acidic, and usually highly colored. Chloride is the principal
dissolved mineral constituent. The low mineral content is due to the
insolubility of the surface sands. The acidic condition of the water
in the southern area is probably due to decomposition of organic
matter and subsequent release of carbon dioxide and humic acids to
the water. The pH of surface water in this area ranged from 4.0
to 5.9 units. The presence of chloride as the principal dissolved
mineral constituent may be due to rain and wind-borne salt from
the coastal area. The chloride concentration is usually less than
12 ppm. High color is caused by organic matter in the water. The
color ranged from 90 to 600 units and was higher than 250 units
most of the time.
The chemical characteristics of water in the Withlacoochee
River near Eva (station 36) indicate no inflows from the Floridan
aquifer to the stream. Between Eva and Dade City (station 40)
the mineral content is higher during periods of low flow but is
essentially the same as that above Eva during periods of high flow.
The highest mineral content observed in this reach of the river
was 302 ppm (see fig. 11). This high mineral content was present
in the river just above the mouth of Gator Creek and is about the
same as the mineral content of the water from the Floridan aquifer
in this area. The hardness of the water at this point was 254 ppm
and the color, 15 units. The principal dissolved mineral constituents
were calcium and bicarbonate.
During periods of low flow, the chemical characteristics of the
water in the Withlacoochee River between Dade City (station 40)
and Trilby (station 42) are similar to those of the water from the
Pasco Packing Company Canal at Dade City. The source of water
in this canal is from wells penetrating the Floridan aquifer. The
mineral content of water in the canal ranged from 182 to 190 ppm.
The color of water in the canal is low (usually less than 10 units),
and the principal dissolved mineral constituents are calcium and

tion of mineral content to discharge at gaging stations in the
Withlacoochee River basin.

(f)
IIl Withlcoochee River
at Rerdell

__ ____ IllIIUII______11~~1 1I-I

REPORT OF INVESTIGATIONS NO. 42

bicarbonate. Additional ground-water inflow in this reach of the
river is indicated. The chemical characteristics of this inflow
indicate that it was derived from the Floridan aquifer.
Gator Hole Slough, a tributary to the Withlacoochee River
downstream from Dade City, was sampled at high flow. The water
was low in mineral content and contained sodium and chloride as
the principal dissolved mineral constituents. The color was 180
units.
Data were collected during the period of low flow (May 23-25,
1961) to determine the quantity and mineral content of the
ground-water inflow in the reach of the Withlacoochee River
between the stations near Lacoochee and Trilby (see fig. 11). The
mineral content of the ground-water inflow from the Floridan
aquifer into this reach of the Withlacoochee River was computed
using the load equation (Hem, 1959):
QIC, + Q2C2 Q3C3
where, Q is the discharge in cfs
C is the mineral content in ppm
QiCi is the instantaneous load near Lacoochee
Q2C2 is the instantaneous load between data-
Collection stations
Q3C3 is the instantaneous load at Trilby
The inflow (Q2) was determined to be 12.2 cfs by subtracting the
discharge near Lacoochee from that at Trilby. The mineral content
(C2) of the inflow was then computed to be 260 ppm which is
approximately equal to that of water in the Floridan aquifer in
this area.
The mineral content of water in the Withlacoochee River at
Croom (station 44) was less than that at Trilby (station 42) or
that at Rerdell (station 43). The difference between the sum of
the discharges at Trilby and Rerdell and that at Croom on May 25,
1961, was 38.9 cfs (see fig. 11). Based on the load equation, the
mineral content of the inflows between the stations would be 148
ppm. Similar computations of data during other periods show
the mineral content of the ground-water inflows in this area to
range from 148 to 174 ppm. The computed mineral content indicates
that the inflow between stations was probably a composite of
surface water and ground-water inflows.
The mineral content of the water in the Little Withlacoochee
River is shown in figure 13f. The color was usually above 100 units
during periods of high flow. The principal mineral constituents
during periods of low flow were calcium-and bicarbonate, the water

FLORIDA GEOLOGICAL SURVEY

was very hard (204 ppm), and the color was low (15 units). These
overall chemical characteristics during low flow indicate inflow
from the Floridan aquifer. The mineral content of water of the
Withlacoochee River at Croom (station 44) varied from 176 ppm
during low flow to 45 ppm during a period of high flow (fig. 13e).
The color ranged from 10 units at low flow to 120 units at high flow.
The water was soft (34 ppm) during high flow and hard (144 ppm)
during low flow.
Data collected at Lake Helene during April 1962 show that the
water was low in mineral content (51 ppm); the temperature
ranged from 760F. at the surface to 680F. at the deepest point in
the lake (25 feet); dissolved oxygen ranged from 7.5 ppm at the
top to 3.8 ppm at the bottom; and the pH ranged from 6.0 units at
the top to 5.3 units at the bottom.
The waters of Lake Mattie and Little Lake Agnes were low in
mineral content and slightly colored. These lakes are similar in
chemical characteristics to those of Lake Helene. The mineral
content of water in the three lakes is about the same as that of
water in the nonartesian aquifer.

OKLAWAHA RIVER BASIN

DESCRIPTION OF BASIN

Palatlakaha Creek is the major headwater stream of the
Oklawaha River. Figure 14 shows a flow diagram of the upper
Oklawaha River system and the names of the various segments of
the water course.
Lake Lowery, the largest of a group of lakes located near Haines
City is the headwaters of the Palatlakaha Creek basin. Most of
the drainage from Lake Lowery is to the north into Green Swamp
Run through a culvert in the old Haines City-Polk City road. At
extremely high lake stages the road is inundated.
The Palatlakaha Creek basin is confined by parallel sand ridges
that extend from Lake Lowery northward almost to Lake Louisa.
Between Lake Lowery and the Polk-Lake County line the drainage
course is called Green Swamp Run. The stream channels in this
water course are not deeply incised, and drainage is through wide
shallow swamps.
Big and Little creeks drain the basin between the Polk-Lake
County line and Lake Louisa. Big Creek is a continuation of
Green Swamp Run. The stream channels for both Big and Little

REPORT OF INVESTIGATIONS No. 42 45

creeks have more definitely incised valleys and the flood plain
swamps are not as.wide.as those for Green Swamp Run.
The Big Creek basin is confined along its eastern boundary by
the Lake Wales Ridge. However, along the boundary between Big

and Little creeks, the ridge is broken by swamps in several places
and the two basins are interconnected. Big Creek, including Green
Swamp Run, drains an area of about 70 square miles. The basin,
from Haines City to Lake Louisa, is about 25 miles long and from
2 to 4 miles wide. The swamp channel ranges in elevation from
about 130 feet near Lake Lowery to about 100 feet near Lake
Louisa.
Little Creek drains an area in Lake County west of Big Creek
and empties into Lake Louisa. The western boundary of the Little
Creek basin is fairly well defined by low ridges. However, in a few
places the ridges are broken by saddles. The exchange of surface
drainage between Little Creek and the Withlacoochee River
through the saddles in the western boundary appears to be
negligible.
The southern boundary of the Little Creek basin is not well
defined. The probable boundary is along an old road that extends
from State Highway 33 to U. S. Highway 27 about a mile or two
north of the Lake-Polk County line. Much of the drainage from
the area that was formerly drained by Little Creek has been
diverted into the Withlacoochee River by interceptor canals. These
canals are located near the Polk-Lake County line. However, some
water from its former basin still drains into Little Creek through
natural swamp channels that were not closed when the interceptor
canals were dug. The present (1962) drainage area for Little
Creek, as outlined in figure 5, is about 15 square miles during dry
periods. During wet periods, water flows into the basin through the
openings in the road along the southern boundary of Lake County.
Lake Louisa is the uppermost of a chain of large lakes in the
upper Palatlakaha Creek system. Lake Minnehaha, Lake Minneola,
and Cherry Lake are next in order below Lake Louisa. These lakes
are connected by the wide, deep channel of Palatlakaha Creek. In
addition to draining these lakes, Palatlakaha Creek also drains an
area of smaller lakes and upland marshes westward to State
Highway 33. This area affords storage facilities for large quantities
of water.
During the latter part of 1956, an earthen dam with two radial
gates was built at the outlet of Cherry Lake to maintain the stages
of the waterway and lakes upstream during prolonged periods of
dry weather. The water surface from the upper pool at this dam
to Lake Louisa is essentially level except during periods of high
discharge. During the maximum discharge period in 1960, the
stage of Lake Louisa was about 1.6 feet higher than that of the

REPORT OF INVESTIGATIONS No. 42

upper pool at Cherry Lake outlet. The fall between Lakes Louisa
and Minnehaha was 0.4 foot during this period.
The channel below Cherry Lake has been improved by a canal
leading into Lake Lucy and Lake Emma. Palatlakaha Creek follows
a more definite channel with steep gradient from Lake Emma to
its mouth at Lake Harris. The fall in this reach is about 32 feet
in 12 miles.

STREAMFLOW

Streamflow data. for gaging stations in the Palatlakaha Creek
basin during the data-collection phase of the investigation are
summarized in table 6.
The flow-duration curve for Big Creek near Clermont (station
3), adjusted from the short-term period to the 311/-year period,
1931-62, is shown in figure 15. Long-term records for the
Withlacoochee River at Trilby (station 42) were used for the
adjustment because discharges at other long-term downstream
stations on the Oklawaha River are partly regulated by
water-control structures.
Streamflow of the headwaters of the Palatlakaha Creek
upstream from Lake Louisa is unregulated. Since 1956, the flow
below Lake Louisa has been regulated by a water-control structure
at the outlet of Cherry Lake. During periods of low rainfall, most
of the drainage from the 160-square mile basin above Cherry Lake
Outlet is stored in the chain of large lakes and marshes between
Lake Louisa and Cherry Lake.
Comparison of peak discharges during floods in March 1960
and September 1960 in Big Creek, Little Creek, and the upper
Withlacoochee River shows the effect of the interconnections
between the Little Creek and the Withlacoochee River basins. The
peak discharge for the March 1960 flood in Big Creek at station 3
was 628 cfs. The discharge in Little Creek measured at station 6
near the peak of this flood was 801 cfs. The higher discharge from
the smaller drainage area of Little Creek indicates that most of the
flow was draining from the Withlacoochee basin into Little Creek
through saddles in the drainage divide.
The peak discharge during the flood of September 1960 for Big
Creek at station 3 was 691 cfs. The concurrent flood peak for Little
Creek at station 5 was 400 cfs. The flood peak for Withlacoochee
River near Eva (station 36) was 2,160 cfs in March 1960 and 1,290

cfs in September 1960. Little Creek serves as an outlet for much of
the flood drainage from the upper Withlacoochee River basin.

CHEMICAL CHARACTERISTICS OF SURFACE WATER

Waters of Big and Little Creeks have chemical characteristics
similar to those of the Withlacoochee River upstream from State
Highway 33 in that they have very low mineral content and are
highly colored. Figure 16a shows that the mineral content of
water in Big Creek ranges from 19 to 61 ppm. Figure 16b shows
that the mineral content of water in Little Creek ranges from 18
to 31 ppm. Color of water in Big Creek ranges from 65 to 240
units and that of Little Creek ranges from 150 to 300 units. Both
streams usually contain sodium and chloride as their principal
dissolved mineral constituents.
Waters of the two streams differ in chemical characteristics in
that water of Big Creek is more mineralized, usually less colored,
and the pH is higher than that of Little Creek. The higher mineral
content of water in Big Creek is due mostly to higher concentrations
of calcium and bicarbonate.

HILLSBOROUGH RIVER BASIN

RELATION TO GREEN SWAMP AREA

The Withlacoochee-Hillsborough overflow channel (C-9, fig. 5),
previously described with the Withlacoochee River basin, is one of
the major drainage outlets from Green Swamp during high flows
and is generally considered to be the head of the Hillsborough River.
The overflow channel as it leaves the Withlacoochee River is about
a mile wide. The road fill and bridge of U. S. Highway 98 crosses
the channel about 1 mile downstream from the Withlacoochee
River. The entire flow is confined by the road fill to the bridge
opening which is 200 feet wide.
White (1958, p.19-24) presents evidence to support an
assumption that the Withlacoochee-Hillsborough overflow channel
was formerly the main channel of the Hillsborough River and that
the Withlacoochee River was once the headwaters of the
Hillsborough River. Field studies made in the area in 1962 by
Altschuler and Meyer indicate that the Withlacoochee-Hillsborough
River overflow was formed prior to natural divergence of the

50 FLORIDA GEOLOGICAL SURVEY

headwaters of the Hillsborough River to the Withlacoochee River
and that the divergence may be related to uplift in the area.
From the bridge on U. S. Highway 98, the Hillsborough River
flows generally southwestward through Pasco and Hillsborough
counties and empties into Hillsborough Bay 531/2 miles downstream.

5CC

too7

so
50

301 ----
2CO -- -- -- -- -- -_-- -- -- -- ---

20

us r
to

"Note -Curv has b- adj-usted
I ----81-- -
,." --T--.--\-,--

Sfrom the short--erm period,
S1958-62, to a 3 I/2 -year
3 i base period

PERCENT OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED
Figure 15. Flow-duration curve for Big Creek near Clermont, 1931-62.

The lower 15 to 18 miles of the river passes through the City of
Tampa. The city water supply is a reservoir created by a dam in
the river 10.2 miles upstream from the mouth. Tampa is vulnerable
to damages from floods in the Hillsborough River because of
extensive development of property in the flood plain.

STREAMFLOW

A summary of streamflow data for the gaging station on
Withlacoochee-Hillsborough overflow (station 39) is shown in table
5. The flow-duration curve is shown in figure 10. No flow occurs
in the channel at this point about 65 per cent of the time.
Crystal Springs flows into the Hillsborough River in southern
Pasco County near the Pasco-Hillsborough County line. The average
flow of Crystal Springs (station 31) is 62 cfs, ranging from 20.3
cfs to 147 cfs. Downstream from Crystal Springs the base flow of
Hillsborough River is well sustained. The flow of Hillsborough
River near Zephyrhills (station 33), which includes flow from
Blackwater Creek, is reported to be 71 cfs or more for 90 percent
of the time (Menke, 1961, p. 29).

CHEMICAL CHARACTERISTICS OF SURFACE WATER

The chemical characteristics of water of the Hillsborough River
upstream from Crystal Springs are similar to those of the
Withlacoochee River between Eva and Dade City although the
mineral content is somewhat higher.
The water of the Hillsborough River at the Withlacoochee-
Hillsborough overflow contained calcium and bicarbonate as the
principal dissolved mineral constituents. The water contained
color that ranged from 80 to 150 units. The mineral content ranged
from 41 to 121 ppm.
The water of Crystal Springs had a mineral content of about
170 ppm, was clear, and contained calcium and bicarbonate as the
principal dissolved minerals. The water was hard and alkaline.
During the periods of low flow, the chemical characteristics of
the water of the Hillsborough River near Zephyrhills (below
Crystal Springs) are essentially the same as those of water of
Crystal Springs. Figure 17 shows the relation of the mineral
content to discharge. During periods of high flow the mineral
content of water is low. A more detailed discussion of the chemical
character of the water of the Hillsborough River is given in a
report by Menke (1961, p. 28-36).

REPORT OF INVESTIGATIONS NO. 42

5000

*

5o2 **I
aDO *S
a 1000
zco 500

40 60 80 100 120 140 160 180 200
MINERAL CONTENT, IN

PARTS PER MILLION
Figure 17. Relation of mineral content to discharge, Hillsborough River near
Zephyrhills.

KISSIMMEE RIVER BASIN

RELATION TO GREEN SWAMP AREA

The eastern boundary of the Green Swamp area is U. S.
"Highway 27 atop the Lake Wales Ridge. This is generally the
surface drainage divide between Palatlakaha Creek in the St. Johns
River basin and headwater tributaries of the Kissimmee River.
The surface drainage from only 5 square miles of the Green
Swamp area flows eastward into the Kissimmee River basin.
Piezometric maps in figures 35 and 36 indicate ground-water move-
ment eastward from the Green Swamp area into the Kissimmee
River basin.

STREAMFLOW

Horse Creek is one of the Kissimmee River tributaries adjacent
to Green Swamp. Streamflow records of Horse Creek at Davenport
(station 19) were collected to study the base flow that is derived

FLORIDA GEOLOGICAL SURVEY

from ground water. The drainage area at the gaging station is
22.8 square miles. The maximum discharge during 2 years of data
collection was 358 cfs and the minimum was 0.5 cfs. Runoff
characteristics of the Horse Creek basin are compared with those
of the Pony Creek basin in a following section of this report.

CHEMICAL CHARACTERISTICS OF SURFACE WATER

Data concerning the chemical characteristics of water in the
Kissimmee River basin were collected from Horse Creek and Reedy
Creek.
Water of Horse Creek is more mineralized than water in the
upper Withlacoochee River. Figure 18 shows the general relation
of mineral content to discharge. The mineral content from July to
November 1960 ranged from 22 to 64 ppm (from daily conductivity
records). Calcium and bicarbonate were the principal dissolved
mineral constituents. The surface materials in the Horse Creek
basin are sands and clays, which are essentially insoluble in water,
and therefore the calcium bicarbonate type water in Horse Creek
is probably due to seepage from the Floridan aquifer. The following

equations were used to determine the approximate amount of
seepage from the aquifer:
Q1 + Q2 = Q
33Q1 + 167Q2 = CQ
where, Q1 is the component of discharge from nonartesian
aquifer and from direct runoff
Qs is the component of discharge from Floridan
aquifer
Q is total discharge of Horse Creek
C is mineral content of water of Horse Creek
33 is average mineral content of ppm of typical water
from nonartesian and from direct runoff
167 is average mineral content in ppm of typical water
from the Floridan aquifer.
Based on the computation, seepage from the Floridan aquifer
averaged about 6 cfs for the 4 complete months of daily conductivity
records.
Color of water in Horse Creek ranged from 60 to 160 units and
the pH ranged from 6.4 to 7.4 units.
Mineral content of water from Reedy Creek during a wet period
in 1959 was 33 ppm, the color 80 units, and the pH 6.0 units.

PEACE RIVER BASIN

RELATION TO GREEN SWAMP AREA

The Peace River basin lies immediately to the south of the
designated boundary for the Green Swamp area. Before construc-
tion of levees, highway and railroad fills, ditches and other drainage
improvements, Lake Lowery and the surrounding marsh apparently
drained southward into Peace River as well as northward to the
Palatlakaha Creek and the Withlacoochee River basins. Under
present conditions, the surface runoff from only 7 square miles of
the Green Swamp area drains southward into the Peace River basin.
This small area includes Gum Lake and its marsh outlet and Lake
Alfred. The headwaters of the Peace River basin lie immediately
south of the highest artesian water levels in the southeastern
part of the Green Swamp area. Piezometric maps in figures 35 and
36 indicate ground-water movement southward to the Peace River
basin.

FLORIDA GEOLOGICAL SURVEY

STREAMFLOW

During the flood of September 1960, caused by Hurricane Donna,
Lake Lowery reached a maximum stage of 133.32 feet above mean
sea level. During this flood, a road fill between a marsh in the
Withlacoochee River headwaters and Gum Lake marsh washed out
and an undetermined amount of water flowed southward into the
Peace River basin through an opening 12 feet wide (C-4, fig. 5).
The flow at Gum Lake marsh outlet (station 22) includes the
drainage from 4.2 square miles in the Gum Lake basin plus that
diverted from the Withlacoochee River basin through opening C-4.
During the flood of September 1960, the peak discharge was not
determined but most of this flood discharge was from the
Withlacoochee River basin. The 3' x 8' box culvert and a section
of the highway at the gaging station were overtopped. The flood
peak reached a stage of 132.0 feet above mean sea level, as
determined from high water marks at the gage. During periods
of low rainfall there is no flow in this channel. For the period May
1961 to June 1962, the channel was dry. The average discharge at
station 22 was 0.55 cfs in 1961. There was no flow from Lake Alfred
during the period April 1961 to June 1962. The total surface
outflow from the Green Swamp area to the Peace River basin is
negligible except during flood periods.

DIVERSIONS AND INTERCONNECTION OF BASINS

Although surface drainage from the Green Swamp area follows
rather definite routes and although the drainage divides are
generally determined by the topographic features, there are several
places where the basins are interconnected and water is diverted
from one basin to another. Some of these points of diversion have
been mentioned under the foregoing discussion of the individual
drainage basins. The hydrologic importance of these intercon-
nections, which are integral parts of the drainage systems, is
shown in the following discussion.
The arrows on the map in figure 5 locate and show the direction
of flow through many of the saddles in the drainage divides. The
interconnections that are shown on the map are the most important
ones disclosed by the investigation, but they by no means include
all such points in the small subbasins where there are no definite
drainage divides.
One of the major diversionary channels is the Withlacoochee-
Hillsborough overflow in southeastern Pasco County (C-9, fig. 5).

REPORT OF INVESTIGATIONS NO. 42

This diversion was discussed in detail under sections describing
the Withlacoochee River and Hillsborough River basins.
Other major interconnections of basins are near the Polk-Lake
County line (C-3) in the eastern part of the Green Swamp area.
The sand ridges in this area are dismembered by a transverse
network of swamps that connect the Withlacoochee River and Little
Creek basins. The alignment of the swamps and the relative widths
of the flood plains shown on aerial photographs indicate that, in
the former natural state, water carried to this area from the south
was discharged by either of three different routes-Big Creek,
Little Creek, or Withlacoochee River. The evidence indicates that
most of the drainage from the southeastern area ran off via Big
and Little creeks.
Beginning about 1948 and continuing progressively each year,
extensive land reclamation by property owners has considerably
altered the pattern of drainage in the eastern area. These physical
changes, which were made for the development of the area,
apparently changed the proportion of the water that drained by
the three routes. Based entirely on the present pattern of drainage
canals and without any factual data on the streamflow from the
upper basins prior to the development of the area, it appears that
the most significant change has been a decrease in the area drained
by Little Creek and an increase in the area drained by the
Withlacoochee River.
Major canals near the Polk-Lake County line were dug about
1948 and 1949 and appear to have intercepted the greater part
of the flow from an area of about 60 square miles that was formerly
the headwaters of the Little Creek basin. This area is roughly 18
miles long and 3 to 4 miles wide. It extends from the present
southern divide of the Little Creek basin southward almost to the
town of Lake Alfred. The greater part of the water from this area
now drains to the Withlacoochee River. However, as discussed in
the description of the Palatlakaha Creek basin, some flow still
enters the Little Creek basin from its former headwaters. The
changes in the drainage system predate streamflow records in the
headwater basins. Therefore, the change in proportion of drainage
between the two basins and the increased effectiveness of the
drainage system may be inferred only on the basis of long-term
streamflow records at downstream gaging stations. The runoff
under present conditions, as compared with the runoff that occurred
during the earlier years, is discussed under the heading "Effects
of Man-Made Changes" in the following section.

FLORIDA GEOLOGICAL SURVEY

A levee now fills a saddle in the drainage divide between Green
Swamp Run and the Withlacoochee River in northeastern Polk
County south of the Polk-Lake County line (fig. 5). Prior to the
construction of the levee (about 1956 or 1957), drainage from Green
Swamp Run divided into flow westward into the Little Creek basin
(now the Withlacoochee River basin) and flow northward into Big
Creek basin.
Lake Lowery and swamps in the upper Withlacoochee River
basin are connected by a natural saddle (C-1) in the confining ridge
northwest of the lake. This saddle is 200 to 300 feet wide and is
one point at which flow may be diverted between the Palatlakaha
Creek and Withlacoochee River basins. At high stages the two
basins are interconnected at this point. Apparently water may flow
through this saddle in either direction, depending on the
distribution of rainfall and the relative water levels in the basins.
There are four interconnections (C-2) between Big and Little
creeks. These openings, all in Lake County, are small and their
net exchange of water is probably negligible in comparison with the
total flow from the basin.
Other places, shown on the map in figure 5, where basins are
interconnected are: (C-4) between the Withlacoochee River
headwaters and Peace River headwaters; (C-5, C-6, C-7) between
Lake Mattie, Withlacoochee River, and Pony Creek; and (C-8)
between the Withlacoochee River and Devils Creek. Many of these
interconnections act as equalizing channels through which water
may flow in either direction, depending on relative water levels in
connected basins.

EFFECTS OF MAN-MADE CHANGES

Many of the physical changes that have been made on the land
surface through man's efforts have already been described. The
most extensive developments of the area have occurred in recent
years, but the first changes in the hydrologic characteristics
undoubtedly occurred several years ago when logging trails and
tramroads were built and much of the native timber was cleared
from the area. The early developments of the area cannot be
evaluated as they predate the period of data collection, but they
probably had only minor effects on the hydrology.
Changes in the drainage characteristics of the Green Swamp
area can be detected by comparing the hydrologic data for years
before drainage developments with the data collected since major

REPORT OF INVESTIGATIONS No. 42

developments have been made. Long-term records of rainfall and
streamflow in the upper Palatlakaha Creek (stations 11 and 12)
and Withlacoochee River (station 42) have been used to detect
changes or trends in the pattern of discharge from the upper
Palatlakaha Creek basin since 1946.
Double-mass curves of cumulative measured runoff and
cumulative computed runoff have been plotted to provide a means
of examining the records of streamflow from the area of
investigation to detect changes that may have occurred (Searcy
and Hardison, 1960). The variables used in preparing the curves
shown in figure 19 are the values of cumulative computed runoff,
taken from the precipitation-runoff relations in the figures on
pages 97 and 99 and cumulative measured runoff at each of the
two gaging stations.
The rainfall pattern is not affected by the progressive changes
in the drainage system in the Green Swamp area. The theoretical
or computed runoff based on rainfall is taken from an average curve
for several years of record. Any change in slope in the double-mass
curves of figure 19 would reflect progressive man-made changes in
runoff.
Figure 19a is the double-mass curve for the Withlacoochee
River basin above the Trilby gaging station. Straight lines are
drawn to average several points that show definite trends. These
lines change in slope between 1942 and 1943, between 1945 and
1946, and between 1953 and 1954. The two changes in slope in the
1940's indicate changes in the runoff pattern but the authors have
no knowledge of the causes of such changes. Minor deviations of
the plotted yearly values of runoff are probably caused by variations
of rainfall distribution and intensity during the year and are not
necessarily indications of changes in the long-term trends. Yearly
values of runoff for 1954-61 define an average line with less slope
than that for any previous period. This change in slope indicates
that a higher rate of runoff from the basin occurred during 1954-61
than that indicated from the same rainfall pattern of previous
years.
Figure 19b is the double-mass curve for the upper Palatlakaha
Creek basin. The figures of annual runoff were adjusted for changes
in storage in lakes. For the period 1946-49, the curve takes the
general direction .as shown by the straight line. However, after
1949, a definite break occurs in the slope of the average line
indicating, less runoff from the area.

60 FLORIDA GEOLOGICAL SURVEY

Figure 19c has been plotted to show the cumulative runoff from
the combined Withlacoochee River and Palatlakaha Creek basins.
The average line defining this curve has the same slope for the
entire period, 1946-61. This indicates that there has been no
significant change in runoff from the combined basins.

The explanation for the significant decrease in runoff from the
Palatlakaha Creek basin is a decrease in the size of the drainage
area. Such a change in the headwaters of Little Creek, a tributary
to Palatlakaha Creek, occurred during the period 1948-49 and has
been discussed earlier in this report. This change has resulted in
the diversion of part of the flow from the Little Creek basin into
the Withlacoochee River basin. The gain to the Withlacoochee
River basin is not as obvious as the loss from the Palatlakaha
Creek basin because of the difference in size of the drainage basins.

GROUND-WATER ACCRETIONS TO STREAMFLOW IN
HORSE AND PONY CREEK BASINS

Stream flow consists of direct surface runoff and ground-water
runoff or base flow. Surface runoff is rainfall that drains directly
into the stream channel during and after a storm. Ground-water
runoff is rainfall that infiltrates to the ground and then discharges
into a stream channel. In well-drained basins surface runoff ceases a
few days after the occurrence of rainfall, and streamflow is then
derived entirely from ground-water runoff. Surface contributions
to streamflow continue for longer periods in basins containing
lakes, swamps, or other surface storage features.
Daily streamflow records were collected for the period June
1960 to June 1962 for Horse Creek at Davenport (station 19) and
Pony Creek near Polk City (station 38). The runoff of these two
streams probably represents the maximum variation in runoff of
streams in the Green Swamp area. Horse Creek and Pony Creek
basins have generally similar characteristics of geology and rainfall,
but the two basins are situated differently with respect to the
piezometric high. The basin slope of Horse Creek is higher than
that of Pony Creek. Pony Creek basin above gaging station 38 is
entirely atop the piezometric high. Horse Creek above gaging
station 19 lies adjacent to the southeastern boundary of the Green
Swamp area (fig. 5) and downslope from the piezometric high
(fig. 35) in an area of artesian flow as indicated by hydrographs in
figure 23.
Graphs of monthly rainfall and runoff in inches for the Horse
and Pony creeks basins for July 1960 to June 1962 are shown in
figures 20 and 21. Base flows, expressed in inches of runoff from
the two basins, were estimated for the low runoff period from
November 1960 to June 1962. Base-flow recession curves were
developed and used as a partial basis for separation of the

FLORIDA GEOLOGICAL SURVEY

14.6" 14.5"

Totals for 1961:

inches
Rainfall 37.2
Runoff 6.41
Base flow 4.90

-1

|AS1960|INID
1 1960

IM[AIMIJIJIAISIOINIDIJIFIMIAIMILI

1961

I 1962

Figure 20. Graphs of monthly rainfall and runoff for July 1960 to June 196i
and estimated base flows for November 1960 to June 1962, Horse Creek al
Davenport.

.I

0
E
10
LU

REPORT OF INVESTIGATIONS No. 42

14.6"

142" _

10 --\----___

I VI

9 -1___s o_ __

Totals for 1961:

-8 inches

Rainfall 38.4
Runoff .79
7 Base flow .39

5i -----i

4

JIAISO ND JFMAMJ JAS ND J FMAMJ
1960 1961 1962

Figure 21. Graphs of monthly rainfall and runoff for July 1960 to June 1962
and estimated base flows for November 1960 to June 1962, Pony Creek near
Polk City.

a,
-o
cn

-2
-90
9E
to
Ui
wU

FLORIDA GEOLOGICAL SURVEY

streamflow into the two component, base flow and direct runoff. The
methods of separating streamflow into its components of base flow
and direct runoff are hypothetical and the results are generally
subject to some limitations. During months of high runoff, July to
October 1960, streamflow was mostly from direct runoff and base
flows could not be estimated with any degree of reliability.
Monthly values of rainfall and runoff for Horse Creek and Pony
Creek are summarized in table 7. Direct runoff was computed as
the difference between total runoff and base flow. For the months
of July, August, and September 1960, the average rainfall on the
Horse Creek basin was 38.8 inches and the runoff was 13.0 inches.
For the same period, the rainfall on the Pony Creek basin was 32.1
inches and the runoff was 19.4 inches. The greater runoff from
Pony Creek resulted from less rainfall than that which occurred
in the Horse Creek basin. This was probably caused by high
ground-water levels in the Pony Creek basin and lack of storage
capacity in the nonartesian aquifer as indicated by comparison of
the hydrographs of wells in the basins (see fig. 23, well 810-136-2;
and fig. 27, well 813-149-2).
Comparison of the data for the year 1961 for the two stations
in table 7 shows that Horse Creek received 37.2 inches of rainfall
and Pony Creek received 38.4 inches. However, the runoff from
the Horse Creek basin was 6.41 inches as compared to 0.79 inch
from Pony Creek. The base flow or ground-water runoff for Horse
Creek was 4.90 inches which was 76 percent of the total runoff.
The base flow of Pony Creek was 0.40 inch which was 51 percent
of the total runoff. Most of the additional runoff for Horse Creek
in 1961 was probably gained by ground-water inflow. Base flow of
the stream was sustained even during prolonged periods of little
rainfall. On the other hand, Pony Creek basin is on top of the
piezometric high and the stream received no ground-water flow
during prolonged periods of low rainfall in 1961 and 1962.
Flow-duration curves based on the 2 years of record for Horse
Creek and Pony Creek are shown in figure 22. A comparison of the
runoff characteristics for the two basins may be made from these
curves. The curves have not been adjusted to a long-term base
period, and therefore should not be used to estimate future
long-term patterns.

AQUIFERS
Aquifers are classified as either nonartesian or artesian.
Nonartesian aquifers are unconfined, and their water surface (the

water table) is free to rise and fall. Artesian aquifers are saturated,
confined or semi-confined, and their water surface is not free to
rise and fall. The water in an artesian aquifer is under pressure
(greater than atmospheric) which causes it to rise above the top
of the aquifer. The level to which water will rise in tightly cased
wells, penetrating an artesian aquifer, is called the piezometric
surface.

The principal importance of an aquifer is its ability to transmit
and store water. The coefficients of permeability (P) and
transmissibility (T) are measures of the capacity of an aquifer to
transmit water. Permeability is usually determined by laboratory
measurements of a minute part of the aquifer, whereas transmissi-
bility usually determined in the field by aquifer tests, represents
the average permeability for a localized area of the aquifer.
The coefficient of storage (S) is a measure of the capacity of
an aquifer to store water. The coefficient of storage for artesian
aquifers is usually determined by pumping tests and may range
from about 0.00001 to 0.001. The coefficient of storage for
nonartesian aquifers can be determined by pumping tests or
laboratory methods and may range from about 0.05 to 0.30 and, for
all practical purposes, equals the specific yield.
Coefficients of permeability were determined by laboratory
analysis for samples from the nonartesian and artesian (Floridan)
aquifers in the Green Swamp area (see tables 8 and 9). Aquifer
tests were made at selected sites and the data were analyzed to
determine coefficients of transmissibility using (1) the type curve

of the nonequilibrium formula (Theis, 1935), (2) the family of
leaky aquifer curves (Cooper, 1963), or (3) a modified
nonequilibrium formula (Jacob, 1950).
Semi-confining beds that impede the movement of ground water
comprise what is commonly called an aquiclude. Ground water will
move through an aquiclude under hydrostatic pressure. For
instance, when the water table is higher than the piezometric
surface of an artesian aquifer, the potential leakage is downward
(recharge to the artesian aquifer) and vice versa. The rate at
which ground water moves through the aquiclude depends on the
vertical permeability and the hydraulic gradient across the
aquiclude.
The aquifers of the Green Swamp area are discussed in order
of occurrence from land surface downward: (1) the nonartesian
aquifer; (2) the secondary artesian aquifer; and (3) the Floridan
aquifer.

NONARTESIAN AQUIFER

DESCRIPTION OF THE AQUIFER

The nonartesian aquifer is composed of undifferentiated plastic
deposits (table 4) which consist of fine-to-coarse-grained quartz
sand with varying amounts of kaolinitic clay.
On the eastern side of the Green Swamp area (see fig. 8, A-A'),
the aquifer ranges from about 50 to more than 100 feet in thickness.
The permeability and specific yield is higher in the vicinity of the
ridges than in the central and western areas. A relatively thin
aquiclude, consisting of clay, forms the base of the aquifer.
On the western side of the Green Swamp area, the aquifer
ranges in thickness from 0 to about 50 feet. An aquiclude consisting
of sandy clay which thickens eastward and grades into the sand of
the nonartesian aquifer forms the base.

RECHARGE AND DISCHARGE

Ground water in the nonartesian aquifer is recharged primarily
by local rainfall. It is discharged by (1) evapotranspiration, (2)
flow into streams and lakes, (3) downward leakage into the Floridan
aquifer, and (4) outflow to areas of lower head outside of the Green
Swamp area.

FLORIDA GEOLOGICAL SURVEY

Most of the nonartesian ground water in the Green Swamp area
is discharged by evapotranspiration because the water table is
relatively close to the surface and surface drainage is poor.
Evapotranspiration losses are least in the sandy ridge areas that
rim the Green Swamp because the water table is farther beneath
the ground than in the interior.
Ground water percolates downward from the nonartesian aquifer
to recharge the underlying Floridan aquifer because the water table
is usually at a higher elevation than the piezometric surface
as shown by the hydrographs in figures 23-29 and the aquiclude
(undifferentiated clay) between the aquifers is relatively thin (see
fig. 8) and permeable. The coincidence of areas of high water table
and of high piezometric head is evidence of leakage. The amount
of ground water that percolates downward is equal to the net
outflow of artesian water from the underlying Floridan aquifer.
The quantity of ground water leaving the Polk piezometric high
in the Green Swamp area, hence leakage from the nonartesian
aquifer, is presented in the table on page 116.
Nonartesian ground water moves laterally to contribute to the
surface runoff from the area. The direction of movement is
generally governed by the topography. Therefore, ground-water
divides in the nonartesian aquifer closely coincide with surface
drainage divides shown in figure 5 except along the eastern
boundary of the area where some nonartesian ground water flows
laterally beneath the Lake Wales Ridge eastward to the Kissimmee
River basin. The quantity of nonartesian ground water leaving the
Green Swamp area by lateral seepage beneath the ridge was
estimated to be insignificant in the water-budget analysis.
Fluctuations of the water table were recorded in several shallow
wells and water-table lakes in and near the southern and eastern
parts of the area, shown in figures 23-29. No data were obtained in
the western part because the nonartesian aquifer is thin or absent.
The hydrographs of wells in the nonartesian aquifer are presented
with hydrographs of wells in the secondary artesian or Floridan
aquifers to show the hydraulic relation between aquifers and the
potential movement of water in a vertical direction.
No long-term records of water-table fluctuations are available
within the Green Swamp area. However, records of water levels
in a well located southeast of the Green Swamp area (810-136-2)
show that the highest and lowest water levels since 1948 occurred
during the period of investigation.

Water levels in most wells in the Green Swamp area show rises
in response to local daily rainfalls. Only wells 810-136-2 and
815-139-3, located in the sandy ridges east of the Green Swamp
area, show no response to local daily rainfall. Apparently, this is
due to the high retention of the thick section of sand through which
the water must percolate to reach the water table.
Hydrographs of water levels in wells located in the central
part of the Green Swamp area (figs. 27 and 28; wells 813-149-2,
813-150-2, 814-143-2, 822-149-2, 832-154-2) show that the water
table declined less than 5 feet from a wet to a dry period (1959-62).
During the wet years of 1959 and 1960, the water table remained
near the surface and the aquifer afforded little capacity to store
7 89

Figure 28. Hydrographs of water -levels in wells (821-202-3; 822-149-1, 2;
832-154-1, 2) in north-central Green Swamp; in a well .(826-211-1) 5 miles

north of Dade City; in wells (822-138-1, 2) -17 miles north of Haines. City;
and in a well (833137-2) 7 miles east ofClermont.
76

959 860 956 862
Figure 28. Hydrographs of water levels in wells (821-202-3; 822-149-1, 2;
832-154-1, 2) in north-central Green Swamp; in a well (826-211-1) 5 miles
north of Dade City; in wells (822-138-1, 2) 17 miles north of Haines City;
and in a well (833-137-2) 7 miles east of Clermont.

REPORT OF INVESTIGATIONS NO. 42

Well 810-14A-2 .
N'onortesion oquifer 2
134

132

Floridon aquifer 10

126
1301 -

-12
124

1960 1961 1962
Figure 29. Hydrographs of water levels in wells 810-144-1, 2 and of Lake
Lowery and Lake Mattie.
additional rainfall. Therefore, the runoff was high. Although the
hydraulic gradient between the water table and the piezometric
surface indicated that water moved downward most of the time, a
reversal in direction was noted for dry periods.
Hydrographs of water levels in wells in the southwestern part
of the Green Swamp area (fig. 25, well 805-155-1 and fig, 26, well
808-155-2) show that the water table fluctuated between 5 and 10
feet during the period 1959-62. The water table remained near the
surface during the wet years of 1959 and 1960, and the aquifer
afforded little capacity for storing rainfall. During the dry years
of 1961 and 1962, the water table was progressively lowered by
pumping from the Floridan aquifer south of the Green Swamp.

FLORIDA GEOLOGICAL SURVEY

The area of greatest decline was in the vicinity of well 808-155-2
where the secondary artesian aquifer is absent. Large fluctuationF
of the water table in this area indicate good recharge to the
Floridan aquifer and good hydraulic connection between the
aquifers.
Hydrographs of water levels in wells east of the Green Swamp
area (figs. 23, 27, and 28, wells 810-136-2, 815-134-2, 815-139-3, and
822-138-2) show that the water table fluctuated between 5 and 10
feet during the period 1959-62. The water table occurs at depths
ranging from about 2 feet to more than 70 feet below land surface.
The area has a potentially large capacity to store rainfall. Water
moves downward from the nonartesian aquifer to the Floridan
aquifer in the Lake Wales Ridge and moves upward in the valleys
of Davenport and Reedy creeks. The best hydraulic connection
between aquifers in the eastern part of the Green Swamp area
probably occurs beneath the Lake Wales Ridge. This is indicated
by almost identical fluctuations of water levels in wells 815-139-2,
-3 (fig. 27).
Water levels in wells and sinkhole lakes, located in the
southeastern part of the Green Swamp area, fluctuated about 5
feet (fig. 29). During wet periods, the water level is near or above
land surface and water is stored in lakes and swamps. During dry
periods, water levels decline due to lack of recharge and to pumping.
Water levels in the nonartesian aquifer are generally higher than
the piezometric surface indicating recharge to the Floridan aquifer.

HYDRAULICS OF THE NONARTESIAN AQUIFER

Permeability of a 3-foot section of the nonartesian aquifer
was determined in a well (810-144-2) in southeastern Green
Swamp and in a well (815-134-2) 5 miles east of Green Swamp by
using the slug test method (Ferris, 1962). The field coefficients of
permeability for the wells were determined to be about 50 gallons
per day per square foot (gpd/ft2) and about 40 gpd/ft2,
respectively. The results of laboratory tests of disturbed sand
samples collected from a test hole in the bottom of Lake Parker
near Lakeland (Stewart, 1959) ranged from 20 to 180 gpd/ft2
(table 8). The permeability of the aquifer is probably lower in the
interior of the Green Swamp area than in the surrounding ridges
because of greater clay content.
The specific yield of the nonartesian aquifer was determined
using a graphical analysis of rainfall and water-table fluctuations

REPORT OF INVESTIGATIONS No. 42

.n wells located generally along the eastern and southern bounda-
ries and in the interior. Continuous records of water-level fluctua-
tions and rainfall were collected at each well site. The data were an-
alyzed to select short periods during which all of the rainfall was
assumed to reach the water table. One or two-day periods were se-
lected when (1) antecedent conditions compensated for moisture
requirements of the unsaturated material above the water table;
(2) the water table was far enough below the ground to store all
the rainfall and none left as runoff; and (3) the rainfall was of
short duration, high intensity, and widespread. The rise in the wa-
ter table is directly proportional to the depth of rainfall. The spe-
cific yield of the aquifer therefore is inversely proportional to the
ratio of rise in the water table in inches to the depth of rainfall in
inches.

EXPLANATION
Plots of change in water level ofter selected
periods of rainfall recorded at same well.
----- Line represents the overage change in water level.

Specific yield = average slope X 100

, Figure 30. Graphical determination of specific yield.

FLORIDA GEOLOGICAL SURVEY

The specific yield of the sand comprising the nonartesian aquifer
ranged from 31.0 to 43.9 percent by laboratory analysis (table 8)
and from 12.5 to 47 percent by analysis of water-level fluctuations
caused by local rainfall, shown in figure 30.
The highest values (22.2 and 47 percent) are considered to be
representative of the aquifer in the sandy ridges that surround
the eastern and southern part of the Green Swamp area. The lower
values (12.5 and 18 percent) are considered to be representative
for the clayey sands in the central portion of the area.

CHEMICAL CHARACTERISTICS OF NONARTESIAN GROUND WATER

Water in the nonartesian aquifer in the eastern part of the
Green Swamp area is less mineralized than that in the Floridan
aquifer. The mineral content of water from the shallow wells in
this area, ranging from 30 to 50 ppm, is due to the low solubility
of the sand and clay which comprise the aquifer. The principal
dissolved mineral constituents are sodium and chloride. The iron
content ranged from 0.19 to 4.0 ppm. The 4.0 ppm in water from
well 808-139-1 was the highest found in the Green Swamp area.
The color of water from wells in the area was less than 15 units
which is lower than that of surface water.
In the western part of the area, the nonartesian aquifer is
almost nonexistent. The chemical characteristics of water in most
shallow wells and in the Floridan aquifer are similar.

SECONDARY ARTESIAN AQUIFER

RELATION TO GREEN SWAMP AREA

The secondary artesian aquifer is composed of interbedded
limestone in the undifferentiated clay (table 4). About 36 feet of
the aquifer is present in well 810-144-1 in the southern part of the
Green Swamp area. The aquifer thickens southward from the
southern boundary of the area and is an important source of
artesian water in southern Polk County. The aquifer pinches out
northward and is absent in most of the Green Swamp area.
The aquifer is recharged by downward percolation of water from
the overlying nonartesian aquifer and discharges principally by.
downward leakage to the Floridan aquifer.
Fluctuations of the piezometric surface of the secondary
artesian aquifer were recorded in well 805-155-3 (fig. 25) and the

REPORT OF INVESTIGATIONS NO. 42

surface is between the water. table of the nonartesian aquifer and
the piezometric surface of the Floridan aquifer. The clay beds
separating the aquifers are leaky as indicated by the conformance
of the fluctuations of the piezometric surfaces.

FLORIDAN AQUIFER

DESCRIPTION OF THE AQUIFER

The Floridan aquifer is the principal source of artesian ground
water in Florida. In the Green Swamp area, the aquifer is exposed
at the surface in the western and northwestern parts and occurs
at depths ranging from 50 to more than 200 feet below land surface
in the eastern part, shown in figure 31.
The Floridan aquifer is composed of marine limestones that have
been exposed to erosion and solution weathering. The formations
that comprise the aquifer in the Green Swamp area range in age
from middle Eocene to Oligocene (table 4). The Geologic cross
sections (fig. 8) show the limestone aquifer and the position of the
overlying plastic material.
The top of the aquifer is highest (90 to 100 feet above msl) in
the west-central part of the area as shown in figure 32. The base
of the aquifer was determined by the first major occurrence of
gypsum. Apparently, the gypsum fills the pores in the lower part
of the Avon Park Limestone. The existing data indicate that the
aquifer is about 1,000 feet thick in the central part of the area.
The transmissibility of the Floridan aquifer will vary depending
primarily on the occurrence of solution features such as caverns,
cavities, and pipes. The presence of dolomite in the limestone is an
indication of solution activity. Dolomite zones and cavities
generally occur in the Inglis Formation and the Avon Park
Limestone which are highly permeable. Logs of numerous wells in
the Green Swamp area indicate that a large percentage of the
cavities in the aquifer contain sand which reduces the transmissi-
bility. The low yields of some wells in the Lake Wales Ridge area
are attributed to sand-filled and clay-filled caverns.

RECHARGE AND DISCHARGE

The Floridan aquifer in the Green Swamp area is recharged by
rainfall that percolates downward from the surface of the ground
either through the nonartesian aquifer and aquiclude or directly

FLORIDA GEOLOGICAL SURVEY

into the Floridan aquifer in outcrop areas. Water is discharged
from the aquifer by (1) outflow to areas of lower piezometric head,
(2) seepage and spring flow into the streams, (3) upward leakage
to the nonartesian aquifer in areas of artesian flow, (4)
evapotranspiration, or (5) pumpage.
Piezometric maps of the area were made from water-level
measurements in about four hundred wells. These maps were
analyzed to determine areas of recharge and discharge and the
direction and rate of ground-water movement.
The first piezometric map of peninsular Florida was prepared
by Stringfield (1936) and the latest, figure 33, was prepared by
Healy (1961).
Ground water moves from high head to low head in a direction
perpendicular to the contour lines. Piezometric mounds, referred
to as "highs," usually indicate areas of recharge to the aquifer.
Piezometric depressions or troughs, referred to as "lows," usually
indicate areas of discharge from the aquifer. Recharge and
discharge may take place anywhere from the high to the low
where geologic and hydrologic conditions are favorable. Therefore,
there is no one point of recharge nor one point of discharge. The
difference in head between contour lines divided by the distance
between them is the hydraulic gradient of the piezometric surface.
The hydraulic gradient varies because of (1) unequal amounts of
recharge or discharge, (2) differences in permeability within the
aquifer, (3) differences in thickness of the aquifer, or (4) boundary
conditions within the aquifer.
Ground water in the central part of the Florida Peninsula moves
outward in all directions from an elongated piezometric high that
extends approximately from central Lake County to southern
Highlands County, generally referred to as the "Polk high," and
from a smaller piezometric high in Pasco County, commonly
referred to as the "Pasco high." The Green Swamp area occupies
a relatively small part of the Polk high. The top of the Polk high
occurs within the southeastern part of the Green Swamp area.
Ground-water drainage areas in the Floridan aquifer do not
coincide with the surface-water drainage areas in the Green Swamp,
shown in figure 34. The ground-water divides in the aquifer shift
slightly in response to recharge and discharge. Therefore, the
positions of the divides as shown in figure 34 were considered to be
average for determining the size of the ground-water drainage
areas that contribute outflow from the Green Swamp area toward
the major surface drainage areas. Water in the Floridan aquifer

REPORT OF INVESTIGATIONS NO. 42

moves generally from the southeastern part of the Green Swamp
area eastward toward the Kissimmee River Basin; westward toward
the Hillsborough and Withlacoochee River basins; southward
toward the Peace and Alafia River basins; and northward toward
the St. Johns River basin.
Figures 35 and 36 show the shape of the piezometric surface of
the Floridan aquifer in the Green Swamp area and vicinity during
a wet period (November 1959) and during a dry period (May 1962).
Analysis of the maps shows the direction of movement of ground
water did not change appreciably from wet to dry periods but the
elevations of the piezometric surface declined. The decline was
greatest along the southern and western borders and least in the
interior of the Green Swamp area. Lows or troughs in the
piezometric surface indicate that ground water discharges into
Withlacoochee River through a spring at the mouth of Gator Creek
and downstream from Dade City; into Hillsborough River at Crystal
Springs; into Blackwater Creek; into Davenport and Reedy Creeks;
and into Horse Creek. Closed depressions, such as those in the
vicinity of Lakeland, indicate the effects of pumping.
Natural hydraulic gradients, indicated by the spacing of the
contour lines in figures 35 and 36, are steep toward the Hillsborough
River on the western side of Green Swamp and toward Reedy,
Davenport, and Horse Creeks on the eastern side. The base flow
of Hillsborough River below Crystal Springs is sustained by more
than 50 cfs of ground-water inflow from the Floridan aquifer. The
base flows of streams on the eastern side of the area are sustained
by relatively small amounts of ground-water inflow from the
Floridan aquifer. Obviously then, the steep gradient toward the
east is caused by some factor other than a high rate of
ground-water discharge. The geology along the eastern side of the
Green Swamp area (see fig. 8, A-A') suggests that the steep
eastward gradient is due to a barrier, or constriction in the aquifer,
that was formed by natural grouting (sink-hole collapse and
cavity-fill) along the fractures and joints in the limestone. Thus,
the barrier effect decreases the ground-water outflow and a piezo-
metric high is formed along the eastern side.
Figure 37 shows the decline in the piezometric surface from the
wet period (1959-60) to the dry period (1962). Water levels
declined least in the interior of the Green Swamp, in the
Hillsborough River basin, and in the Kissimmee River basin
(Davenport, Horse, and Reedy-creeks). Water levels declined most
along the southern (near Lakeland), western (near Dade City),

FLORIDA GEOLOGICAL SURVEY

and northeastern boundaries. Water levels declined about 5 feet in
discharge areas (Hillsborough and Kissimmee River basins)
because the ground-water discharge is relatively uniform regardless
of seasonal variations in rainfall. Water levels declined less than 5
feet in the interior of the Green Swamp because there was little
local pumpage and the rainfall during the dry period was about
enough to balance the outflow; therefore, the aquifer remained
relatively full.
The area surrounding the Green Swamp is more populated and
developed and increased pumping during the dry period (1962)
caused a greater decline in piezometric levels than would have
occurred under natural conditions. If there had been no appreciable
increase in pumping, the map could be used to detect areal changes
in the hydraulic characteristics of the aquifer, particularly changes
in permeability.
The northernmost extent of an area of heavy pumping for
mining, industrial, municipal, and irrigational supplies is in the
vicinity of Lakeland where the water levels declined about 20 feet.
The drawdown is confined to the southern boundary of Green
Swamp, suggesting that the area of the sinkhole-riddled ridges
around southern Green Swamp is a recharge area. Water levels
declined between 10 and 20 feet on the western side of Green
Swamp in the vicinity of Dade City. This is considered to be an
area of high permeability and good recharge. Water levels declined
about 10 feet in the northeastern area which is also considered to
be an area of high permeability and good recharge.
The general conclusion is that increase in discharge (natural
or pumping) does not appreciably increase the lateral movement
of ground water from the interior of Green Swamp but does affect
the border areas.

HYDRAULICS OF THE FLORIDAN AQUIFER

Coefficients of horizontal and vertical permeability were
determined for selected core samples of the limestones that
comprise the Floridan aquifer. The samples were obtained from
well 805-154-8, located just north of Lake Parker. The laboratory
determinations are presented in table 9. The permeability values
ranged from 0.0001 to 19 gpd/ft2. The specific yields ranged from
0.2 to 23.2 percent. However, the specific yield determined in the
laboratory represents that of the rock sample and not of the aquifer
as confined.

REPORT OF INVESTIGATIONS NO. 42 83

Pumping tests were conducted in Green Swamp area and
vicinity to determine coefficients of transmissibility (T) and storage
(S) for the Floridan aquifer. The results of the tests are presented
in table 10. Values of T ranged from about 20,000 gpd/ft to about
700,000 gpd/ft. The storage coefficients ranged from 0.013 to 0.0018
which means that for 1 foot change in head of the piezometric

TABLE 10. Pumping test data (Floridan aquifer)

Aquifer Average field
Coefficient Coefficient penetration coefficient of
transmissibility Coefficient of leakage (nearest permeability
Well number gpd/ft) of storage (gpd/ft2/ft) ten feet) (gpd/ft2)

surface, the aquifer releases or takes into storage 0.013 to 0.0013
foot of water per square foot of surface area of the aquifer.
A comparison of the results of laboratory tests with pumping
tests indicate that the permeability of the Floridan aquifer is
largely dependent upon the presence of solution holes (caverns,
pipes, etc.) which, of course, are not represented in the small core
samples.

-- --- --
------ B----------

Davenport- Horse Creek area
Eastern area
Northwestern area
Southwestern area
Dode City area

I I I I I I I

I I I I I I I I

i0300
^0.000

III I I I I III I

100,000
COEFFICIENT OF TRANSMISSIBILITY
(gpd/ft)

1,0OO00,000

Figure 38. Graphs showing the relations between coefficient of transmissibility
and depth of penetration in the Floridan aquifer.

The values of T for the pumping tests in table 10 were plotted
against depth of aquifer penetration, as .shown in figure 38. The
wide range in values of T are caused by unequal penetration and by
areal and vertical variations in permeability. Areal analysis of
the data indicate that generally the eastern side (Davenport-
Horse Creek area) of the Green Swamp area has a low value of T
and the western side (Dade City) has a high value of T. Therefore.
the test data were evaluated by location and depth of penetration.

REPORT OF INVESTIGATIONS No. 42

The average field coefficients of permeability (Pf) table 10) were
averaged for each area and then multiplied by the approximate
thickness of the aquifer (1,000 feet) to estimate the coefficient of
transmissibility (Te) for each representative area. The data were
analyzed for (1) the Davenport-Horse Creek area east of the Lake
Wales Ridge; (2) the eastern area, which includes the general area
between State Highway 33 and U.S. Highway 27; (3) the
northwestern area, which includes the area west of State Highway
33 and north of the Withlacoochee River; (4) the southwestern
area, which includes the area west of State Highway 33 and south
of the Withlacoochee River; and (5) the Dade City area west of the
Withlacoochee River. The results of the computations (expressed
to the nearest hundred thousand gpd/ft) are presented in table 11.
Computations of ground-water movement into or out of the area
used in the water-budget analysis were based on the estimated
coefficients of transmissibility shown in table 11.

Barrier boundaries caused variations in the values of T in the
vicinity of the Lake Wales Ridge. Observation wells 815-139-2 and
815-140-1 were used to observe the effects of drawdown and
recovery caused by pumping well 814-139-5. Water level measure-
ments were also made in the pumped well. The data were analyzed
by the Theis method (1935), the family of leaky aquifer curves by
Cooper (1936), and the Jacob method (1950). The data defined
three curves, figure 39, with T values of 680,000 gpd/ft and
1,150,000 gpd/ft, for the observation wells and 120,000 gpd/ft for
the pumped well. The wide variation in T probably indicates that
the basic assumptions prerequisite for the analysis of the data do
not apply and is probably caused by heterogeneity of the aquifer
and existence of a barrier boundary. The test site is in a faulted
area (see fig. 8, C-C'). Figure 40 shows the location of the wells
with respect to sand-filled fractures in the underlying lime-
stone along the Lake Wales Ridge. The variation in T values
is probably caused by sand-filled fractures which act as barriers

FLORIDA GEOLOGICAL SURVEY

01o I I II I I I I I I I I I 1
10-6 10-5
Time(minutes) / Distance (feet)
a Using Theis method (1935) and Cooper method (1963)

T= 120,000 gpd/ft
Q= 1,600 g.pm.

10 100
TIME, IN MINUTES
b. Using Jacob method (1950) and pumped well.

Figure 39. Graphs of pumping test at a well (814-139-5)
of Haines City.

S11 Upper number is well number
S5 Lower number is the elevation of the
Sn top of the Florldon aquifer, in feet,
o referred to mean sea level.
M4-2 -/00--
SR 54 Contour represents the approximate
t elevation of the top of the Floridon
I Aquifer, in feet, referred to mean
-y 4 19 sea level. Contour interval 100 feet

Figure 40. Map showing environment affecting pumping test at a well
(814-139-5) about 9 miles north of Haines City.

between the pumped well and the two observation wells. The
barriers decrease the drawdown in the observation wells giving
erroneously high values of T. Probably the best value of T was
obtained from data from the pumped well which is comparable to
the results of a nearby test (see table 10, well 816-135-2).

CHEMICAL QUALITY OF WATER IN THE FLORIDAN AQUIFER

The quality of water in the Green Swamp area is good. The
total mineral content is generally less than 350 ppm. Water
containing a mineral content of less than 500 ppm is usable for most
purposes. The water of the Floridan aquifer is more mineralized
(100-400 ppm) than surface water or water from the nonartesian
aquifer (20-50 ppm). The higher mineral content is caused by
contact of water with materials that are more soluble. About 75
percent (by weight) of the mineral constituents dissolved in water
of the Floridan aquifer are calcium and bicarbonate that cause the
water to be hard and alkaline. Hardness, illustrated in figure 41,
is one of the more undesirable characteristics. The water ranges
from moderately hard in the eastern part of Green Swamp to very
hard in the western part.
Figure 42 shows the iron content of water in the Floridan
aquifer in the Green Swamp area. The highest concentrations of

STATE OF FLORIDA
STATE BOARD OF CONSERVATION
DIVISION OF GEOLOGY

FLORIDA GEOLOGICAL SURVEY
Robert O. Vernon, Director

REPORT OF INVESTIGATIONS NO. 42

HYDROLOGY OF GREEN SWAMP AREA IN
CENTRAL FLORIDA

By
R. W. Pride, F. W. Meyer, and R. N. Cherry

Prepared by the
UNITED STATES GEOLOGICAL SURVEY
in cooperation with the
FLORIDA GEOLOGICAL SURVEY,
the
FLORIDA DIVISION OF WATER RESOURCES AND CONSERVATION,
and the
SOUTHWEST FLORIDA WATER MANAGEMENT DISTRICT

Dear Governor Burns:
For many years, it has been thought that much of the recharge
of water to Florida's prolific artesian aquifer occurred in the Green
Swamp area. For this reason, it was believed that a detailed geo-
logic and hydrologic study of the area would be helpful and neces-
sary. I am pleased to report to you that a study, "Hydrology of
Green Swamp Area in Central Florida," prepared by R. W. Pride,
F. W. Meyer, and R. N. Cherry, of the U. S. Geological Survey, in
cooperation with the Division of Geology of the State Board of
Conservation, will be published as Florida Geological Survey Re-
port of Investigations No. 42.
This report provides all of the data necessary for the wise utili-
zation, and perhaps for the preservation, of parts of the Green
Swamp area. It will also assist in the planning for the Four-
Rivers area to alleviate floods and to conserve our water and land.

Respectfully yours,
Robert O. Vernon
Director and State Gcologist

Completed manuscript received
September 9, 1965

Published for the Florida Geological Survey
By the E. O. Painter Printing Company
DeLand, Florida

This report was prepared by the Water Resources Division of
the U. S. Geological Survey in Cooperation with the Florida
Geological Survey, the Florida Division of Water Resources and
Conservation, and the Southwest Florida Water Management
District.
The authors wish to express their appreciation for the
cooperation of the many residents and public officials for
information given during the well inventory and reconnaissance
of the area. Special acknowledgement is due the Florida State
Road Department, the Florida Forest Service, and property owners
who granted permission to drill test wells. The following agencies
made financial contributions for the collecting of data used in this
report: Hillsborough County, Marion County, Pasco County, Polk
County, Sumter County, Lake Apopka Recreation and Water
Conservation Control Authority, Oklawaha Basin Recreation and
Water Conservation and Control Authority, and Tsala Apopka
Basin Recreation and Water Conservation Control Authority.
The calcium carbonate equilibrium study of ground water of
central Florida was based on data collected and analysed in
cooperation with William Back, Geologist, Water Resources
Division, Arlington, Virginia, as part of an investigation of ground
water along the Atlantic seaboard. Contributions to the knowledge
of the geohydrology in the Withlacoochee-Hillsborough overflow
area were made by Z. S. Altschuler, Geologist, Geologic Division,
Washington, D. C. Assistance in the interpretation of electric and
drillers' logs was rendered by C. R. Sproul, Geologist, Florida
Geological Survey.
The work on this project was done under the supervision of
the Florida Water Resources Division Council comprised of A. O.
Patterson, district engineer of the Branch of Surface Water, M. I.
Rorabaugh, succeeded by C. S. Conover, district engineers of the
Branch of Ground Water, and J. W. Geurin, district chemist,
succeeded by K. A. MacKichan, district engineer, of the Branch of
Quality of Water.

Green Swamp is an area of about 870 square miles of swampy
flatlands and sandy ridges near the center of the Florida Peninsula.
The elevation of the land surface ranges from about 200 feet above
mean sea level in the eastern part to about 75 feet in the western
part. The Withlacoochee River drains two-thirds of the area. The
Little Withlacoochee River, the headwaters of the Oklawaha River,
the Hillsborough River, the headwaters of the Kissimmee River,
and the headwaters of Peace River drain the remaining area. The
surface is mantled with a varying thickness of sand and clay which
comprises the nonartesian aquifer. Porous marine limestones
comprising the Floridan aquifer underlie and drain the subsurface.
The Floridan aquifer crops out in the western part of the area and
occurs at depths ranging from 50 to more than 200 feet in the
eastern part. The mineral content of both surface and ground
water does not impair the usability of the water for most purposes.
However, surface water is generally highly colored and acidic, and
ground water is hard and generally contains objectionable amounts
of iron.
Hydrologic data were collected during the period, July 1, 1958,
to June 30, 1962, for making quantitative and qualitative analyses
of the hydrologic budget and for determining the significance of
the hydrology of the Green Swamp area with respect to central
Florida.
Extremely high and unusually low annual rainfalls were
recorded during the period of investigation. The factors of the
water budget for each of the 3 complete years of record, 1959-1961,
show that average rainfall on the area ranged from 70.9 to 34.7
inches; surface runoff ranged from 31.1 to 2.3 inches; ground-water
outflow ranged from 1.8 to 2.2 inches; and water derived from
change in storage ranged from insignificant amounts in 1959 and
1960 to about 4.3 inches in 1961. Evapotranspiration losses, which
were the residuals in the water-budget equation, ranged from 39.1

FLORIDA GEOLOGICAL SURVEY

to 34.5 inches. Surface runoff varied through a wide range from
wet to dry years, while ground-water outflow varied little. The
data show that the annual losses by evapotranspiration varied
little from wet to dry years. Evaporation losses from Lake Helene
amounted to 53.1 inches during 1962.
Comparison of water-budget factors for the eastern and western
parts of the area shows that higher rates of ground-water recharge
to the Floridan aquifer occur in the eastern part.
The amount of annual runoff from the total area has not
significantly changed in recent years. However, the distribution
of the runoff has been changed by drainage canals that divert
some of the flow from the upper Oklawaha River into the
Withlacoochee River.
Impoundment of water in Green Swamp would provide some
flood protection for the lower Hillsborough River and the lower
Withlacoochee River basins. Impoundment of the total discharge
from Green Swamp to the Hillsborough River during the March
1960 flood would have reduced the flood crest at 22nd Street, Tampa,
by about 1 foot. Impoundment of the March 1960 flood discharge
in reservoirs proposed for the Green Swamp area (Corps of
Engineers, 1961) would have reduced the flood crest of the
Withlacoochee River at the Trilby gaging station by about 4 feet
and at the Croom gaging station by about 1.7 feet.
Impoundment of water in Green Swamp Reservoir would have
little effect on ground-water outflow from the total Green Swamp
area because of increased seepage rates beneath the levee, increased
evaporation losses, and because the aquifer under present conditions
is essentially full. Impoundment of water in the Southeastern
Conservation Area (Johnson, 1961) would increase the seepage
rates during dry periods by about 60 percent. Impoundment of
water will become more significant relative to ground-water
recharge as pumpage from the Floridan aquifer increases.
High piezometric levels in the southeastern part of the Green
Swamp area are caused partly by a relatively slow rate of
ground-water outflow due to sand-filled fractures, caverns, and
sinkholes in the Floridan aquifer.
Mineral content and calcium carbonate saturation studies show
that generally the water in the Floridan aquifer in central Florida
is low in mineral content and undersaturated.
Interpretation of quantitative and qualitative data indicate
that recharge to the Floridan aquifer in the Green Swamp area is
about the same as that in other parts of central Florida.

REPORT OF INVESTIGATIONS NO. 42

INTRODUCTION

To satisfy the demands of a rapidly increasing population, many
acres of land in Florida are converted each year to residential and
industrial uses. Urbanization of these areas and the demand for
increasing the food supply thus require that man search for new
areas to develop for agricultural uses. This search, in many
instances, has led to the development of marginal lands.
The Green Swamp area, shown in figure 1, in central Florida
is an area where man is developing agricultural land from marginal
land. The present efforts for its development are similar to the
early efforts for developing the Everglades in that many miles of
canals and ditches have been constructed to improve the drainage.

.Figure 1. Map of Florida showing location of Green Swamp area.

FLORIDA GEOLOGICAL SURVEY

PURPOSE AND SCOPE

Lest the early mistakes of the Everglades be repeated, the
Florida Division of Water Resources and Conservation considered
that an appraisal of the physical and hydrologic features of the
Green Swamp area was needed for future guidance in planning
water-resource policy. Lack of factual hydrologic information has
contributed to the controversy on whether the area should be
utilized for flood control and water conservation or for agriculture.
This investigation provides factual information on the hydrology
of the area for determining the feasibility of either choice of
utilization.
The hydrology of the Green Swamp area was investigated by
the U. S. Geological Survey in cooperation with the Florida
Geological Survey, the Florida Division of Water Resources and
Conservation, and the Southwest Florida Water Management
District. The investigation covered a 4-year period beginning July
1, 1958. A Comprehensive Report on Four River Basins, Florida,
was prepared by the Corps of Engineers in 1961.
The following factual data, used to appraise the hydrologic
significance of the area, were collected during the investigation;
the amount of rainfall on the area; the pattern of surface-water
drainage; the effects of improved drainage channels and man-made
diversions; the amount and direction of surface-water runoff; the
amount and direction of ground-water outflow; the amount of
evaporation losses from an open water surface; the interrelationship
of rainfall, surface water, and ground water; and the chemical and
physical characteristics of water in relation to the hydrologic
environment.
A comprehensive appraisal of the hydrology of the Green
Swamp area and its significance to central Florida have been made
on the basis of the findings of this investigation. The report does
not recommend any plan of development or utilization of the water
resources of the area. An appraisal was made, however, of the
hydrologic effectiveness of a plan of water control and water
conservation proposed by the U. S. Corps of Engineers (1961).

PREVIOUS INVESTIGATIONS

Only cursory investigations of the water resources and geology
of the Green Swamp area were made prior to this investigation.
Few long-term records of streamflow, ground-water levels, and

REPORT OF INVESTIGATIONS NO. 42

chemical quality had been collected in the vicinity as part of the
statewide data-collection programs.
Many of the physical and hydrologic features of the area are
,iven in an interim report by Pride, Meyer, and Cherry (1961).
General descriptions of the geology of the region have been
,iven by Cooke (1945), Vernon (1951), White (1958), and Stewart
:1959). Stringfield (1936) defined and described the principal
artesian aquifer of Florida.
Analyses of water from surface and ground sources in the
vicinity of the Green Swamp area are given in reports by Collins
and Howard (1928) and Black and Brown (1951).

METHODS OF INVESTIGATION

Most of the data for the investigation were collected during
the 4-year period from July 1958 to June 1962 and covered a wide
range of hydrologic conditions.
The investigation of the water resources of the Green Swamp
area involves studies of water in three main physical environments:
(1) precipitation, which occurs as rainfall; (2) surface water, which
occurs on the surface of the ground; and (3) ground water, which
occurs beneath the surface of the ground.
Waters in these environments are interrelated. Thus, it was
necessary to study the whole process or system, rather than any
part, to understand and to evaluate the water resources of the area.
The methods of studying water in each environment are
different. Some characteristics of water in the three environments
may be measured directly; some may be evaluated by analysis of
representative samples from which results may be inferred; and
some characteristics and quantities must be determined indirectly.
For instance, the chemical characteristics of the water at a
particular place can be used as an indication of the environment
through which the water has passed. The surface materials in the
Green Swamp area are relatively insoluble and the surface waters
are therefore low in mineral content. The rock below the surface
materials is relatively soluble and the contained water is
considerably more mineralized. Mineralized streamflow in areas
such as the Green Swamp, where industrial and municipal disposals
into streams are minor, indicates ground-water inflow into streams.
Therefore, the chemistry of the water can be used as a tool to give
more complete evaluation of the hydrology of the area.

6 FLORIDA GEOLOGICAL SURVEY

Daily records of rainfall were collected at 24 stations located as
shown in the figures on pages 2 and 5. Some of these records
are from U. S. Weather Bureau long-term stations. Short-term
rainfall records were collected at stream or well data-collection
stations during part of the investigation using standard 8-inch
gages with tipping-bucket attachments to the water-stage
recorders.
Surface-water characteristics of the area were determined by
collecting stage, streamflow, and chemical-quality data at gaging
stations and at miscellaneous sites; by making field and aerial
reconnaissance of the area; and by studying maps and aerial
photographs.
All surface-water data-collection stations are presented in table
1 and located in figure 2 and in the figure on page 5. The grid
coordinate number shown in column 2 of table 1 is based on the

well-numbering system shown in figure
and stage at 24 sites and of stage of 20
near the area of investigation.

3. Records of streamflow
lakes were collected in or

Information on the quality of surface water was obtained during
high, intermediate, and low flows to determine the general chemical

characteristics and the extremes in quality characteristics during
the period of study. These data were supplemented with a series of
reconnaissances over the entire area generally within a period of

REPORT OF INVESTIGATIONS NO. 42

1 to 3 days. The data were used to determine the quality of water
prevalent in the area at a given time and to help determine the
interrelations between surface water and ground water.
Ground-water characteristics were determined by collecting
data concerning water levels, surface and subsurface geology, and
water chemistry from an inventory of existing wells in the Green
Swamp area and vicinity (fig. 2). Information on the depth of the
well, the amount of casing, and the depth to static water level was
recorded for more than 600 wells. Most of the inventoried wells
penetrated the Floridan aquifer. The approximate elevation of land
surface above mean sea level was determined at each well by use
of either altimeter, topographic maps, or spirit level. These data
were supplemented by selected data collected prior to this
investigation and by test drilling to provide better coverage of
the area.
The well-numbering system that is derived from latitude and
longitude coordinates is based on a state-wide grid of 1-minute
parallels of latitude and 1-minute meridians of longitude, shown in
figure 3.
Instruments were used to record continuously the water-level
fluctuations in the various aquifers. These data were supplemented
by periodic determinations of water levels and chemical character-
istics of water in selected wells in order to evaluate areas of
recharge and discharge for the aquifers.
The wells in which continuous and selected periodic water-level
data, and quality-of-water data were collected, are presented in
table 2.
During the periods October to December 1959 and May to June
1962, water-level measurements were made to prepare piezometric
maps which show the direction of water movement in the Floridan
aquifer. Hydraulic gradients scaled from these maps were used to
infer rates of water movement.
To obtain general information on the occurrence of artesian
and nonartesian ground water in the Green Swamp area, 26 test
wells were drilled at 16 different sites. At 9 of these sites a pair
of wells were drilled (one into the Floridan aquifer and one into
the nonartesian aquifer). A summary of test-well data is presented
in table 3. During the drilling, samples of rock cuttings were
collected. The lithology of the various formations and significant
changes in water levels were recordered in the well log.
Examination of rock cuttings of selected wells were supplemented

Type and
frequency
Well number i County Aquifer of record Period of record

800-153-1 Po F, H Sp December 1954 to May 1962
801-207-1 Hi F A(1) May 1962
802-135-1 Po F Sp November 1957 to February 1960
802-157-12 Po F A(l) March 1962
803-147-4 Po F A (1) March 1962
803-204-1 Hi F Sp May 1958 to May 1962
804-207-1 Hi F Sp November 1956 to May 1962
805-155-1 Po N Sr August 1955 to February 1960
Sp February 1960 to June 1962
805-155-2 Po F Sr March 1956 to February 1960
Sp February 1960 to June 1962
A (1) November 1959
805-155-3 Po H Sr February 1956 to February 1960
Sp February 1960 to June 1962
806-137-6 Po F A (1) March 1962
806-140-2 Po F A(1) November 1959
806-135-3 Po F Sp July 1954 to February 1960
806-156-1 i Po N Sp August 1955 to June 1962
806-156-2 Po F Sp January 1956 to June 1962
807-202-1 Po F A(1) November 1959
808-139-1 Po N A(1) February 1962
808-143-1 Po F A (1) February 1962
808-147-1 Po F A(1) February 1962
808-153-1 Po F Sp January 1958 to May 1962
A (1) November 1959
808-155-1 Po F Sp June 1955 to March 1956
Sr March 1956 to June 1962
A (1) November 1959
808-155-2 Po N Sp June 1955 to June 1962
809-154-4 Po F A(1) February 1962
809-158-1 Po H A(1) February 1962
810-136-1 Po F Sr 1946 to June 1962
(P-44)

REPORT OF INVESTIGATIONS No. 42 13

TABLE 2. (Continued)

Type and
frequency
Well number County Aquifer of record Period of record

810-136-2 Po N Sr 1948 to June 1962
(P-47)
810-144-1 Po F Sp July 1959 to October 1960
Sr October 1960 to June 1962
A(21), July 1959 to April 1962
K(5),
T(4),
B(4)

810-144-2 Po N Sr October 1960 to June 1962
A(3), July 1959 to November 1961
K(2)

810-149-1 Po F A(2) November 1959 to March 1962
810-149-2 Po F Sp January 1955 to May 1962
810-151-2 Po F Sp February 1960 to May 1962
810-207-1 Pa F Sp June 1960 to May 1962
813-147-1 Po F A(1) February 1962
813-149-1 Po F Sr March 1959 to June 1962
A(6) April 1959 to March 1962

813-149-2 Po N Sr April 1959 to June 1962
813-150-2 Po N Sr October 1960 to June 1962
813-201-1 Po F Sp August 1959 to June 1962
A(2) November 1959 to March 1962

814-143-1 Po F Sr October 1960 to June 1962
814-143-2 Po N Sr October 1960 to June 1962
814-148-1 Po F Sp October 1955 to July 1957
Sr July 1957 to April 1959

814-210-1 Pa F A(1) March 1962
814-210-2 Pa F A(1) March 1962
815-134-1 Po F Sp August 1960 to October 1960
Sr October 1960 to June 1962
A(1) March 1962

815-134-2 Po N Sp August 1960 to October 1960
Sr October 1960 to June 1962

815-139-1 Po F A(1) June 1959
815-139-2 Po F Sp August 1960 to October 1960
Sr October 1960 to June 1962

815-139-3 Po N Sr October 1960 to June 1962
815-149-3 Po F Sp July 1960 to November 1960
Sr November 1960 to June 1962
A(1) April 1961
815-157-2 Po F Sp March 1956 to May 1958
Sr May 1958 to June 1962
A (1) November 1959

by interpretation of electric and gamma-ray logs of some wells and
geologists' and drillers' logs of wells which are on file with the
Florida Geological Survey.

GEOGRAPHY

One of the most prominent topographic features in the central
part of the Florida Peninsula is Green Swamp which is an
extensive area of flatland and swampland at a relatively high
elevation. Five major drainage systems originate in or near the
Green Swamp area and flow in several directions to the sea. The
area contains the headwaters of the Oklawaha River, which flows
generally northward to become the largest tributary of the St.
Johns River; the Kissimmee and Peace Rivers that flow southward;
the Hillsborough River that flows southwestward; and the Withla-
coochee River that flows northwestward.

LOCATION

The Green Swamp area is in central Florida (see fig. 1) west
of and adjacent to a high sandy ridge that forms the major axis
of the peninsula. For this study the boundaries of the area were
established arbitrarily and the Green Swamp area should not be
confused with a small drainage basin that is generally known as
Green Swamp Run in the headwaters of the Big Creek watershed
in southern Lake County and northeastern Polk County. The
boundaries of the Green Swamp area, as designated for this
investigation, have been extended to encompass a much larger
area. The project area includes the southern parts of Lake and
Sumter counties, the northern part of Polk County, and the
eastern parts of Pasco and Hernando counties (see fig. 2).
The eastern boundary of the Green Swamp area is U. S.
Highway 27, from Clermont south-southeastward to Haines City.
The southern and southwestern boundaries of the area generally
coincide with the divides separating drainage northward to the
Big Creek and Withlacoochee River basins from drainage south-
ward to the Peace and Hillsborough River basins. These boundaries
follow a meandering line westward from Haines City to a point
two miles north of Lakeland and then northwestward to Dade City.
The western boundary of the area is U. S. Highway 301 northward
from Dade City to St. Catherine. The northern boundary extends
from St. Catherine eastward along the Little Withlacoochee River

FLORIDA GEOLOGICAL SURVEY

basin divide to State Highway 50 and along State Highway 50
eastward to Clermont. The boundaries described enclose an area
of 870 square miles.

TOPOGRAPHY

The Green Swamp area is in the Central Highlands topographic
region as defined by Cooke (1945). The area is bordered on the
eastern side by the Lake Wales Ridge, on the southern side by the
northern termini of the Winter Haven and Lakeland Ridges, and
on the western side by the Brooksville Ridge (White, 1958, pp.
9-11). Figure 4 shows the locations of these ridges.
Although the area is designated the Green Swamp, it is not a
continuous expanse of swamp but is a composite of many swamps
that are distributed fairly uniformly within the area. Interspersed
among the swamps are low ridges, hills, and flatlands. Several
large and many small lakes of sinkhole origin rim the southeastern
and northeastern parts of the area. The elevation of the land
surface ranges from about 200 feet above mean sea level (msl)
in the eastern part to about 75 feet in the river valleys in the
western part.
Prominent topographic features affecting the drainage of the
eastern part of the area are the alternating low ridges and swales
that trend generally north-northwestward from the southern
boundary to the Polk-Lake County line. The ridges parallel the
major axis of the Florida Peninsula and their configuration suggests
that they were formed by subsidence and erosion along fractures
and joints. Aerial photographs of the area between U. S. Highway
27 and the Seaboard Air Line Railroad show five of these long
narrow ridges with intervening swales.
In the western part of the Green Swamp area there is little
evidence of the elongated ridges, and the main land-surface features
are large swamps, flatlands, and rolling hills. There are many
small swamps in patches and strips generally less than half a mile
wide. Most of these swamps support good growths of cypress
trees while in the uplands pine and scrub oak trees grow
abundantly. The largest continuous. expanse of swampland lies
within the valley of the Withlacoochee River and is more than a
mile wide at places. Limestone is exposed in the western part of
the Green Swamp area.

REPORT OF INVESTIGATIONS NO. 42

DRAINAGE

The drainage system of the Green Swamp area and vicinity is
shown on the map in figure 5. The headwaters of four stream
systems within the Green Swamp area, listed in order of their
proportion of the area drained, are: Withlacoochee River, Little
Withlacoochee River, Oklawaha River, and Hillsborough River.
Other streams that head near the boundaries of the Green Swamp
area are: Reedy, Davenport, and Horse creeks in the Kissimmee
River basin; Peace Creek drainage canal and Saddle Creek in the
Peace River basin; Fox Branch in the Hillsborough River basin;
and Jumper Creek Canal and a major canal that head northwest
of Mascotte in the Withlacoochee River basin. Of the total area
of 870 square miles, 710 square miles are drained by the
Withlacoochee River and its tributaries.
The surface drainage of the Green Swamp area is poor because
of the flat topography and lack of well developed stream channels.
Following heavy rainfall, water stands in large shallow sheets over
much of the area.
Boundaries of the elongated north-south drainage basins, in
the eastern part of the Green Swamp area, are formed by low
ridges. The valleys between the ridges are not deeply incised but
their effectiveness as drainage channels has been improved by
many miles of canals and ditches. Some parallel drainage basins
are interconnected in several places by gaps or saddles through
the ridges. Through these gaps water may flow at times from one
stream valley into another. The amount and direction of flow
depend on the relative elevation of water levels in the adjoining
basins and the hydraulic conveyance of the connecting channels.
The canals and ditches, for the most part, have been dug to
follow the natural drainage courses through the shallow swamps.
However, in some places, probably to provide firm footing for the
excavation equipment and to avoid clearing through the dense
growth of cypress trees, the ditches have been dug along the edges
of the large swamps rather than through the interior. Also, to
provide better alignment in some places, the ditches have been cut
through ridges to connect the adjacent swamps. These shortcuts
have bypassed the circuitous natural drainage routes and have
straightened and shortened the courses of the waterways.
Surface drainage from most of the Green Swamp area is
generally toward the north and west. However, the headwaters of
the Peace River basin originate along the southern boundaries of

FLORIDA GEOLOGICAL SURVEY

the area and the flow is generally southward. Along the eastern
boundary of the area, drainage is toward the east and southeast
into the Kissimmee River basin. Other drainage from the Green
Swamp area is toward the southwest into the Hillsborough River
via a natural channel in eastern Pasco County.
The subsurface drainage of the Green Swamp area is generally
poor. Ground-water levels in the interior of the area remain near
the surface most of the time, consequently the aquifers provide
little opportunity to store water from heavy rainfall. Ground-water
levels fluctuate through a greater range in the ridges that form the
eastern, southern, and western boundaries. The wide range of
fluctuation indicates better subsurface drainage and greater storage
capacity along the boundaries than in the interior.
Subsurface drainage is through both the Floridan and the
nonartesian aquifers but most is via the Floridan aquifer. Water
percolates downward from the overlying nonartesian aquifer to the
Floridan aquifer or enters exposed portions of the Floridan aquifer.
Movement of ground water in the Floridan aquifer is generally
outward in all directions from the southeastern part of the area.
However, the areas contributing to the aquifer (p. 80) show that
the predominant directions of ground-water movement are east and
west. The ground-water divides in the aquifer shift slightly in
response to demands in each contributing area. Most of the surface
area that potentially would contribute recharge to the Floridan
aquifer in Green Swamp lies within the Withlacoochee River basin.
The distribution of ground-water outflow originating in each
surface basin is shown in the tables on pages 116 and 117.

CULTURE AND DEVELOPMENT

The Green Swamp area is sparsely populated except for a few
small towns and communities on the ridges along the border and
along State Highway 33.
Most of the land is in large tracts owned by private individuals
or corporations. The only large tract of public land in the area is
the Withlacoochee State Forest, part of which is within the
boundaries of the Green Swamp area in Sumter, Hernando, and
Pasco counties.
The principal industry is agriculture. Much of the upland area
has been cleared and planted in citrus groves. Other upland areas
have been cleared and are used for cattle raising. Very little of
the land is cultivated. The low swampland is unsuitable for

REPORT OF INVESTIGATIONS NO. 42

agriculture because of poor drainage. In spite of the many miles of
ditches, drainage is still inadequate. Even in the cleared areas that
are suitable for agriculture, few attempts have been made to
reclaim the many small, round, cypress swamps that dot the area.
Cypress lumbering was once an important industry in the
western part of the area, particularly in the Withlacoochee River
Swamp where there were extensive stands of trees. The first access
roads to penetrate the interior of the swamp were trails and tram
roads built for cypress lumbering. Timber and pulpwood are now
produced from the pine flatwoods interspersed among the swamps.
There is some development of the mineral resources of the area
for the commercial market. Extensive phosphate deposits in Polk
County lie just south of the Green Swamp area. Some phosphate
is mined within the area but the amount is only a small percentage
of that produced in southern Polk and eastern Hillsborough
counties. Limerock, used in road construction and agriculture, is
mined in the northwestern part of the area. Deposits of sand,
suitable for building uses, are mined in many places in the eastern
part of the area.

CLIMATE

The location of the Green Swamp area, well south in the
Temperate Zone, and its proximity to large bodies of warm water
produce a warm humid climate. Precipitation and temperature, the
principal climatic elements that influence the hydrology of the
Green Swamp area, are described separately.

PRECIPITATION

The study of precipitation in central Florida can be restricted
to rainfall only, because snow and hail are virtually unknown. The
normal or long-term average annual rainfall of the Green Swamp
area is 52.7 inches. This normal is computed by the Thiessen
method of weighting long-term rainfall records at each of the
following U. S. Weather Bureau stations in or near the project area:
Clermont 6 miles south, Lake Alfred Experiment Station, Lakeland,
and St. Leo (figs. 2 and 5).
The average rainfall for the station at St. Leo, west of the area,
is slightly higher than that for the other three stations which are
located farther inland. The average rainfall at the four stations
ranges from a minimum of 50.1 inches at the Clermont station to

FLORIDA GEOLOGICAL SURVEY

a maximum of 56.4 inches at the St. Leo station. In view of the
small deviation of these extreme values from the mean, the
weighted average rainfall of 52.7 inches for the area of
investigation appears to be reasonably accurate.
The amount of rainfall on the area varies seasonally. About
60 percent of the annual total rainfall occurs during the wet season
from June through September. In the spring and early summer,
local thunderstorms of high intensity and short duration sweep
over the area. Showers occur almost daily, or perhaps several times
a day, during June and July. Heavier and more prolonged rainfalls
occur generally in August and September and are often intensified
by tropical storms that occasionally reach hurricane proportions.
On the other hand, there are periods of a month or more with little
or no rainfall. Periods of below average rainfall usually occur
during the winter season from November to February.
During wet years the annual rainfall is about twice that of dry
years. The annual and the mean monthly rainfalls for the years
1931-1961 are shown by bar graphs in figure 6. The maximum
annual rainfall during this 31-year period was 70.9 inches in 1959
and the minimum was 34.7 inches in 1961. Both occurred during the
period of the investigation. It is a fortunate circumstance that the
full range of hydrologic conditions was experienced during the
investigation.

TEMPERATURE

A knowledge of temperature variations in central Florida is
pertinent to a study of its water resources because of the dominant
influence of temperature on rates of water losses by evaporation
and transpiration.
The mean monthly temperature in the Green Swamp area ranges
from 610 F. for January to 82' F. for August. The lowest
temperature recorded during the 69-year period of record at the
Clermont station was 180 F. and the highest was 104 F. Daily
temperatures recorded at the U. S. Weather Bureau stations show
that all parts of the area have essentially the same temperature,
ranging no more than 2 to 30 F.
Killing frosts occur infrequently in this area, and damage to
vegetation, although severe from the standpoint of agriculture,
seldom is great enough to affect the hydrologic factors pertinent
to water supplies.

REPORT OF INVESTIGATIONS NO. 42

tr) Lr 0 L r) ~
-n n 0 Un 0 -
CALENDAR YEAR
CALENDAR YEAR

Rainfall of Green Swamp area
computed from U. S. Weather
Bureau records at four stations,
weighted by Thiessen method
as follows:

Water loss from a drainage basin is the difference between the
average rainfall over the basin and the runoff from the basin for a
given period (Williams, 1940, p. 3). In humid regions, where there
is sufficient water to satisfy the demands of vegetation, the mean
annual water loss is principally a function of temperature
(Langbein, 1949, p. 7). The relation between mean annual

9

8

6

4

3
9- --

FLORIDA GEOLOGICAL SURVEY

temperature and mean annual water loss under such conditions
is shown in figure 7, which is taken from U. S. Geological Survey
Circular 52. For the Green Swamp area where the mean annual
temperature is 72' F., the annual water loss would be 48 inches
according to this figure.

ENVIRONMENTAL FACTORS AFFECTING THE
QUALITY OF WATER

The quality of water in the Green Swamp area reflects the
solubility of the material which the water contacts and its biologic
environment, both of which are natural influences. Surface water
is usually lower in mineral content than ground water because of
low solubility of materials on the surface of the ground and short
time of contact of water with the materials.
The quality of the surface water (lakes, streams, and swamps)
depends mostly on the composition of the precipitation and the

10 20

30 40

50 E0

Natural water loss, in inches
Figure 7. Relation of annual water loss to temperature in humid areas.

80

70

u-
o

0 60

0.
E
50
a5

40

30
30

Polatlakaho Creek above Mascotte
I I I /
Withlacoochee River at Trilby-.

SComputed annual water loss
at two gaging stations in
Green Swamp area.

(After Longbein, W. B., and
others, 1949)
______ _____ I

REPORT OF INVESTIGATIONS NO. 42

biologic environment. Generally, the mineral content of water in
streams varies inversely with discharge. Surface waters are
usually highly colored and acidic. Sodium and chloride, although
in very low concentrations, are the principal dissolved mineral
constituents and may be present as a result of wind and rain-borne
salts from the ocean.
The quality of ground water in the Green Swamp area generally
meets the requirements for most municipal, industrial, domestic,
and agricultural uses. Ground water of lowest mineral content
occurs along the eastern and western boundaries of the area and
is lowest near the lakes. Ground water of highest mineral content
occurs in the central part of the Green Swamp. The principal
dissolved mineral constituents are calcium and bicarbonate which
are products of limestone solution. Relatively high concentrations
of calcium in the water cause hardness which is probably the most
objectionable characteristic of the ground water in the Green
Swamp area.

GEOLOGY'

Topographically, the surface of the Green Swamp area
resembles a basin, or trough, opening to the north. However,
geologically, the Green Swamp is part of an eroded, faulted
anticline. The oldest formations are exposed along the axis of the
anticline and eroded remnants of younger formations rim the flanks
and present a basin-like feature.
The Green Swamp area is underlain by several hundred feet of
limestone and dolomite that have been periodically exposed to
solution-weathering and erosion. The surface is mantled with a
varying thickness of plastic material (sand and clay) that was
deposited in fluctuating shallow seas. No attempt has been made
to differentiate the formations within the plastic material because
of its complexity and the lack of data.
The upper part of the elastic sediments, composed of clayey
sands, forms a distinct hydrologic unit, commonly referred to as
the nonartesian aquifer. The basal portion of the plastic sediments,
composed mostly of clay and some interbedded limestone
(secondary artesian aquifer), is less permeable than the overlying,

1The classification and nomenclature of the rock units conform to the usage
of the Florida Geological Survey and also with those of the U. S. Geological
Survey, except for the Fort Preston Formation (?), the Tampa Formation,
and the Ocala Group and its subdivisions.

FLORIDA GEOLOGICAL SURVEY

clayey sands or the underlying porous limestone. The solution-
riddled limestone formations, which underlie the clay deposits,
comprise the Floridan aquifer, the principal source of artesian
ground water in the State. Where present, the clay forms an
aquiclude which retards the rate of water movement between the
aquifers.
The principal artesian aquifer was first described by Stringfield
(1936) and later named the Floridan aquifer by Parker (1955).
According to Parker, the Floridan aquifer includes those limestone
formations ranging in age from the middle Eocene (Lake City
Limestone) to perhaps early and middle Miocene (Hawthorn
Formation). In the Green Swamp area the following formations
comprise the Floridan aquifer (from youngest to oldest); the
Suwanee Limestone; the Ocala Group which includes the Crystal
River, Williston, and Inglis Formations; and the Avon Park
Limestone. The base of the aquifer is considered to be near the
base of the Avon Park limestone at the first occurrence of gypsum
because the presence of gypsum probably indicates poor circulation
of ground water.

FORMATIONS

The formations that underlie the Green Swamp area are
presented in table 4. Generalized geologic cross sections, shown in
figure 8 were prepared based on data from wells located along lines
A-A', B-B' and C-C'.

UNDIFFERENTIATED CLASTIC DEPOSITS

Undifferentiated plastic deposits, ranging from late Miocene to
Recent in age, underlie the Green Swamp area except in the western
part where Tertiary limestones are exposed at the surface. The
deposits consist primarily of clayey sand or sandy clay. The
following lithologic sequence (from youngest to oldest) is indicated:
(1) fine quartz sand surficiall sand) with varying amounts of clay
and organic material; (2) variegated (red-orange-tan) fine to
coarse quartz sand with little clay; (3) white fine to very coarse
quartz sand with varying amounts of white-green kaolinitic or
montmorillonitic clay; and (4) white silty quartz sand with varying
amounts of mica flakes.
Generally, the deposits range from 100 to 200 feet in thickness
beneath the ridges that rim the Green Swamp area; however, they
are thin or absent in the western part and tend to become more

TABLE 4. Geologic formations and their water-bearing characteristics in Green Swamp area and vicinity.

System Series

Recent
Quaternary

Pliocene

Pleistocene

Upper

Miocene Middle

Lower

Oligocene

Eocene

Upper

Middle

Formation
(after F.G.S.)

Recent
Deposits

Terrace
Sands

Citronelle
Formation

Fort Preston
Formation (7)

Hawthorn
Formation

Tampa
Formation

Suwannee
Limestone

Crystal
River
Formation

0 Williston
g Formation

S Inglis
Formation

Formations
used in this
report

Undifferentiated
Clastic
Deposits

Undifferentiated
Clay

Suwannee
Limestone

Crystal River
Formation

Williston
Formation

Inglis
Formation

Avon Park Avon Park
Limestone Limestone

Approximate
range of
thickness
(feet)

0-200

0- 60

0- 80

0-120

0- 40

0- 50

800-1,000

Lithology

Light-colored clayey
sands grading
into sandy clays

Dark-colored phos-
phatic clay with
limestone lenses

Hard, white-yellow
limestone

Soft, gray,
limestone

Hard, tan
limestone

Hard, tan
limestone

Soft to hard,
white-brown,
dolomitic lime-
stone

Water-bearing
Aquifer characteristics

Non-
artesian

Secondary
artesian

Floridan

Generally poor source in the cen-
tral part of the area. A fair
source in the ridge areas.

Generally very poor except in
the Lakeland area where iriter-
bedded limestones are a fair
source.

Generally good to excellent. The
best source is the dolomitic
Avon Park Limestone. Evapo-
rite (selenite) deposits near
the base of the Avon Park
Limestone is considered to be
the base of the aquifer.

Tertiary

------

FLORIDA GEOLOGICAL SURVEY

clayey where they thin over the crest of the anticline (fig. 8, A-A').
The deposits appear to increase in coarseness from the interior of
the Green Swamp area eastward to the Lake Wales Ridge. Much
of these deposits occur as cavity fill in the underlying limestones
especially in the ridge areas.
The undifferentiated plastic deposits form the nonartesian
aquifer in the area. Generally, the deposits in the western part
of the Green Swamp area are thin or absent, low in permeability
and porosity; and therefore, they are of minor significance as an
aquifer.

UNDIFFERENTIATED CLAY

Undifferentiated clays of Miocene age underlie most of the area,
except in the western part, and contain varying amounts of quartz,
phosphatic sand, and interbedded limestone. The following
general lithologic sequence (from younger to older) is indicated:
(1) light gray-tan-blue-green, montmorillonitic clay with varying
amounts of quartz, phosphatic sand, and interbedded limestone;
(2) dark gray-green-blue phosphatic, silty clay with varying
amounts of quartz pebbles, silt and mica flakes.
The light-colored clay with interbedded limestone is part of the
Hawthorn Formation of early and middle Miocene age. Generally,
its occurrence is limited to the southeastern part of the Green
Swamp area. It thickens eastward and southward and forms a
secondary artesian aquifer which is a significant source of artesian
water outside of the Green Swamp area. The dark, silty clay is
probably equivalent to the Tampa Formation of early Miocene age
(Carr, 1959). Generally, its occurrence is limited to the eastern
part of the Green Swamp area where it forms an aquiclude.

SUWANNEE LIMESTONE

The Suwannee Limestone (Cooke and Mansfield, 1936) of
Oligocene age is a white dense fossiliferous limestone. It is present
in the southern and western parts of the Green Swamp area and
crops out along the Withlacoochee River near Polk-Sumter-Pasco
County line. The formation thickens southward in Polk and
Hillsborough counties and westward in Pasco County. Many of the
springs along the upper Hillsborough River flow from exposures
of Suwannee Limestone. The Suwannee Limestone overlies the
Crystal River Formation and it is overlain by either undifferen-
tiated clay or undifferentiated plastic deposits.

REPORT OF INVESTIGATIONS NO. 42

OCALA GROUP

The Ocala Group (Puri, 1957) includes three limestone
formations of late Eocene age. The subdivisions of the Ocala Group
(from youngest to oldest) are the Crystal River, the Williston,
and the Inglis Formations.

CRYSTAL RIVER FORMATION

The Crystal River Formation is primarily a coquina of large
foraminifers and crops out in an area extending from northern
Polk County through the southern end of Sumter County and into
eastern Hernando County. It ranges from 50 to 120 feet in
thickness, except in the eastern part of the area where it is absent.
In the central part of the area, the formation contains many
sand-filled cavities.

WILLISTON FORMATION

The Williston Formation is a tan-cream, medium to hard
limestone containing abundant micro-fossils. The formation is
slightly coarser than the underlying Inglis Formation but generally
finer than the overlying Crystal River Formation. In most of the
area, the Williston Formation ranges from 20 to 40 feet in thickness.
It is thin or absent along the eastern boundary of the area.

INGLIS FORMATION

The Inglis Formation is generally a white-tan, hard, fossil-
iferous limestone. The texture of the formation appears to be finer
than that of the Crystal River and Williston Formations. In most
of the area, the Inglis Formation is about 50 feet thick. It is thin
or absent along the eastern boundary of the Green Swamp area.

AVON PARK LIMESTONE

The Avon Park Limestone (Applin and Applin, 1944) of late
middle Eocene age was the deepest formation penetrated by test
drilling. The formation is nearest the surface on an upthrown
fault block along the eastern side of the area (fig. 8, A-A'). The
formation is found at considerable depth in the area south and
southwest of Green Swamp. The top of the formation is

FLORIDA GEOLOGICAL SURVEY

characterized by a distinct color change from tan to brown
limestone and by abundant cone-shaped foraminifers. The formation
is a brown, dolomitic, porous limestone. Selenite (gypsum) near
the base of the formation probably forms the bottom of the
Floridan aquifer. The Avon Park Limestone is highly permeable
and is the main source of water for most of the high-capacity wells
in the area. Figure 9 shows the configuration of the top of the
Avon Park Limestone. The map shows the northwest-southwest
trend of the faulted anticline.

STRUCTURE

The Peninsular arch (Applin, 1951), a buried anticlinal structure
of Paleozoic sediments, trends generally north-northwestward and
its main axis is located east of the Green Swamp area. A flexure,
developed on the western flank of the Peninsular arch in the
Tertiary limestones, is called the Ocala Uplift. The Green Swamp
area is located at the southern end of the Ocala Uplift (figs. 8
and 9).
Vernon (1951) dated the Ocala Uplift as post-Oligocene in age.
Faults in the Green Swamp area complicate the definition of the
geology and the hydrology. The main area of faulting occurs
along the Lake Wales Ridge. Faulting in this area was described
by Vernon (1951, p. 56) and named The Kissimmee Faulted Flexure.
The cross sections in figure 8 show vertical displacement along
fault zones.
The faults are probably post-Oligocene. Subsequent movement
along fault zones may have occurred over a long period of time,
the later movements being associated primarily with subsidence
and sinkhole collapse along the solution-widened zones.
Figure 9 shows a structural map based on the top of the Avon
Park Limestone. The contour lines generally define the shape of
the anticline with associated faults. The linearity of ridges on the
anticline suggests that other faults exist in the area.
Faulting probably could affect the hydrology of the Green
Swamp in the following ways:
(1) Joints or faults within the Floridan aquifer, widened by
solution, could cause zones of high permeability, or could cause
zones of low permeability when filled with plastic materials.
(2) Displacement along the faults could position formations
of different lithology (hence permeability) one against the other,

The water supply of the earth, whether it is on the surface or
below the ground, has its origin in precipitation. Of the
precipitation that reaches the ground, part is returned to the
atmosphere by evapotranspiration; part remains above ground and
is stored temporarily in lakes, ponds, and swamps, or moves to
the sea as streamflow; and part percolates into the ground, some
to replenish the soil moisture and some to enter the zone of
saturation and recharge the ground-water aquifers. Ground water
moves in the aquifers under the influence of gravity, towards areas
of discharge such as streams, lakes, springs, wells and the oceans.

WITHLACOOCHEE RIVER BASIN

DESCRIPTION OF BASIN

The'Withlacoochee River drains 82 percent of the Green Swamp
area. The total drainage area at stations 42 and 43 at the western
boundary is 740 square miles, all of which is within the project
area except for 45 square miles of lakes and hills west of U. S.
Highway 301 and south of U. S. Highway 98 near Dade City.
Most of the general topographic and drainage features of the
Green Swamp area, described in preceding sections of this report,
apply to the Withlacoochee River basin in particular. The following
description of the basin refers specifically to this stream system.
The Withlacoochee River heads in a group of lakes and swamps
in the north-central part of Polk County in the vicinity of Polk
City and the town of Lake Alfred (see fig. 5). Lakes Van and
Juliana, the uppermost of these headwater lakes, drain into Lake
Mattie. Surface drainage from Lake Mattie spills through a wide
shallow marsh along the northeastern shoreline and flows
northward through a series of interconnected shallow swamps and
ditches to the northern boundary of Polk County. This is generally
considered to be the major headwater channel of the Withlacoochee
River. Other headwater tributaries originate in the marshes
between Lakes Mattie and Lowery and flow generally northward
between the confining ridges. These channels join near the

FLORIDA GEOLOGICAL SURVEY

northern boundary of Polk County and flow westward to form the
Withlacoochee River.
West of State Highway 33 the tributaries of the Withlacoochee
River are not confined by the ridges that are prominent in the area
east of the highway. These tributaries have developed basins that
are generally more fan-shaped than those in the eastern part.
Pony Creek, which flows northwestward, is the first of the large
tributaries entering the Withlacoochee River west of the Seaboard
Air Line Railroad. Pony Creek heads in a swamp east of Lake
Helene near Polk City. Lake Helene has no surface outlet except
at extremely high stages when it overflows into the Pony Creek
basin.
Grass Creek, the next large tributary, empties into the
Withlacoochee River about one mile downstream from Pony Creek.
Grass Creek heads in a group of small lakes in the vicinity of Polk
City. the largest of which is Lake Agnes. The outlet from Lake
Agnes is a ditch leading from the northern end of the lake and
connecting with the network of canals and ditches that carry the
water northwestward through the swamp. Several other tributaries
flow into Grass Creek as it crosses the swamp.
Gator Creek empties into the Withlacoochee River at the
Polk-Pasco County line. This is the largest tributary upstream
from the diffluence of the Withlacoochee River to the Hillsborough
River. Gator Creek heads in several small swamps northeast of
Lakeland and flows northwestward through a network of swamp
channel and ditches.
From the point of diffluence to the Hillsborough River, the
channel of the Withlacoochee River turns abruptly to the north and
continues northwestward to the western boundary of the Green
Swamp area at U S. Highway 301.
About 14 miles downstream from the point of diffluence, a major
canal draining several lakes and swamps east of Dade City empties
into the river from the west. This canal also carries the drainage
from an area of hills and lakes west of Dade City and the effluent
from citrus concentrate plants at Dade City.
One of the larger tributaries entering the Withlacoochee River
from the east is formed by the confluence of Devils Creek and
Gator Hole Slough. Devils Creek heads in a swamp about 21/
miles east of the Sumter-Pasco County line. At high stages some
water from the Withlacoochee River moves through a gap in a low
ridge into Devils Creek. This water returns to the Withlacoochee
River farther downstream.

REPORT OF INVESTIGATIONS NO. 42

Gator Hole Slough heads just east of the Seaboard Air Line
Railroad and flows westward through an unimproved swamp
channel, entering the eastern boundary of the Withlacoochee State
Forest about 3 miles west of the railroad. It continues within the
boundaries of the Forest to its confluence with Devils Creek which
empties into the Withlacoochee River 21/ miles farther west.
The Little Withlacoochee River, the largest tributary of the
Withlacoochee River, heads near State Highway 33 in Lake County
and flows westerly. Bay Root Slough is the headwater tributary
of the Little Withlacoochee River. This stream carries the drainage
from several lakes and swamps east of the Seaboard Air Line
Railroad and flows northwestward to the Lake-Sumter County line
at the eastern boundary of the Withlacoochee State Forest. The
river channel within the Forest is wide and shallow and contains
dense growths of cypress trees. The channel has been allowed to
remain in its natural swampy condition to store as much water as
possible, rather than to remove the water by improved drainage,
as a precautionary measure against fire damages to the valuable
cypress and pine trees in the Forest. The Little Withlacoochee
River emerges from the Forest near the Sumter-Hernando County
line, where it is joined on the north by a major canal. This canal
drains a swampy area between the Forest and State Highway 50.
The river continues westward through the swamp to the crossing
of State Highway 50 where it turns and flows northwestward
toward U. S. Highway 301. Another canal joins the river about a
quarter of a mile upstream from U. S. Highway 301. This canal
heads near Webster, flows southward about 11 miles, then turns
westward to Big Gant Lake and then to the Little Withlacoochee
River. The Little Withlacoochee River continues westward and
empties into the Withlacoochee River 3 miles downstream from
U. S. Highway 301.
STREAMFLOW

Streamflow data for gaging stations in the Withlacoochee River
basin during the data-collection phase of the investigation are
summarized in table 5.
Flow-duration curves for five gaging stations in the Withla-
coochee River basin are given in figure 10. Records for only the
Trilby gaging station are continuous for the 311/2-year period,
1931-62. The curves for the other four stations in the basin have
been adjusted from their individual short-term records to the
31/-year base period.

TABla1 5. Streamflow data for Withlacoocheo River basin gaging stations in Green Swamp area
(see figure 5 for station locations)

Drainage Discharge in chf
Station area Calendar Runoff
number Station (yd.ml.) year Maximum Minimum Mean in Inches

The flow-duration curves indicate the percentage of time that
specified discharges were equaled or exceeded during the period
of record. These may be considered probability curves used to
estimate the percent of time a specified discharge will be equaled
or exceeded in the future. The use of flow-duration curves to
indicate the future pattern of flow from a basin is valid only if the
climatic conditions remain the same and the amount and
distribution of runoff from the basin is not significantly changed
by man.
The flow-duration curve for Withlacoochee River at Trilby
(station 42) may be only an approximate representation of duration
of future low flows because of the progressive increases in
ground-water inflow by pumpage above the gaging station.
However, the flow-duration curves for the other four stations
shown in figure 10 may be considered probability curves and used
to estimate the percent of time that a specified discharge will be
equaled or exceeded in the future.
During a period of extremely low flow on May 23-25, 1961,
streamflow was measured and water samples for chemical analysis
were collected at several sites on the Withlacoochee River. The
results of this low-flow investigation are shown on the map in
figure 11.
The base flow of the Withlacoochee River near Dade City
(station 40) represents the natural drainage from 390 square miles
because no surface flow is diverted to the Hillsborough River basin
through the overflow channel, C-9. Since about 1941 or 1942, the
effluent from citrus processing plants at Dade City has been drained
into the Withlacoochee River by way of the Pasco Packing Company
canal. The water used by these plants is pumped from deep wells.
Measurements at station 41 of the effluent from the Pasco Packing
Company canal during 1958-62, ranged from 5 cfs, when the plant
was at minimum operation, to about 76 cfs at peak operation during
the citrus packing season. Inflow to the river from this plant and
others at Dade City produces higher discharge below station 40
east of Dade City than would be derived from the natural yield of
the basin. During dry periods, the effluent at Dade City greatly
exceeds the base flow of the Withlacoochee River (see fig. 11).
The drainage area above Trilby (station 42) comprises
two-thirds of the Green Swamp area and the record collected at this
station is a good index of the long-term variations of surface runoff
from the entire area except at low flow.

REPORT OF INVESTIGATIONS No. 42

The discharge at the Trilby gaging station does not represent
the natural runoff from the Withlacoochee River basin because of
the high-water flow diverted from the basin to the Hillsborough
River by the Withlacoochee-Hilisborough overflow channel (C-9)
and the effluent into the river from the citrus concentrate plants
at Dade City. When the Withlacoochee River reaches a stage of
about 78.5 feet above msl at the overflow channel, part of its flow
is diverted into the Hillsborough River. At high stages more than
a fourth of the flow from the upper Withlacoochee River is diverted
through this channel. Computations of basin runoff for either the
Withlacoochee or the Hillsborough Rivers must be adjusted for the
amount of discharge from one basin to the other. Percentagewise,
the plant effluent into the basin is small except when the discharge
in the Withlacoochee River is extremely low and the plant is at peak
operation.
The annual and mean monthly discharges at the Trilby gaging
station are shown by the bar graphs in figure 12. The general
relation between rainfall and streamflow is evident from figures 6
and 12. During the wet years of 1959 and 1960, annual rainfall over
the Green Swamp area was 70.9 inches and 69.5 inches, respectively.
The annual mean discharge at the Trilby gaging station was 1,157
cfs for 1959 and 1,209 cfs for 1960. The higher runoff for 1960 was
probably the result of a carry-over from the high rainfall of 1959.
The maximum discharge of record at the Trilby station was
8,840 cfs on June 21, 1934. Flood-frequency studies by Pride (1958)
indicate that the recurrence interval of a flood at this magnitude
is more than 100 years. The peak discharge of the flood of March
1960 was 6,920 cfs and was the third highest flood of record. The
recurrence interval of a flood of this magnitude is about 40 years.
The drought of 1954-56 was the most severe dry period of
record, considering its 3-year duration and yearly deficiencies.
Annual rainfall on the basin above the Trilby station for 1954-56
was 39.9, 40.2, and 46.2 inches per year, respectively. The prolonged
period of low rainfall resulted in low discharges at the Trilby
station during each of the 3 years. The lowest annual mean
discharge at the Trilby station was 75.4 cfs for 1932, a year in
which the total rainfall amounted to 39.6 inches. The total annual
rainfall on the basin in 1961 amounted to only 35.2 inches and was
the minimum for any year of record. Effluent from citrus
concentrate plants, derived from ground-water sources, accounted
for the higher annual mean discharges for 1954-56 and 1961 than
that for 1932.

The graph of mean monthly discharge for the Withlacoochee
River at Trilby (fig. 12) shows that runoff from the basin is lowest
for the months of November through June. The season of highest
runoff is the 4-month period, July through October. During these
months, 58 percent of the runoff from the basin occurs.

CHEMICAL CHARACTERISTICS OF SURFACE WATER

Waters of the Withlacoochee River in the eastern part of the
Green Swamp area are very low in mineral content (figure 13
a, b) acidic, and usually highly colored. Chloride is the principal
dissolved mineral constituent. The low mineral content is due to the
insolubility of the surface sands. The acidic condition of the water
in the southern area is probably due to decomposition of organic
matter and subsequent release of carbon dioxide and humic acids to
the water. The pH of surface water in this area ranged from 4.0
to 5.9 units. The presence of chloride as the principal dissolved
mineral constituent may be due to rain and wind-borne salt from
the coastal area. The chloride concentration is usually less than
12 ppm. High color is caused by organic matter in the water. The
color ranged from 90 to 600 units and was higher than 250 units
most of the time.
The chemical characteristics of water in the Withlacoochee
River near Eva (station 36) indicate no inflows from the Floridan
aquifer to the stream. Between Eva and Dade City (station 40)
the mineral content is higher during periods of low flow but is
essentially the same as that above Eva during periods of high flow.
The highest mineral content observed in this reach of the river
was 302 ppm (see fig. 11). This high mineral content was present
in the river just above the mouth of Gator Creek and is about the
same as the mineral content of the water from the Floridan aquifer
in this area. The hardness of the water at this point was 254 ppm
and the color, 15 units. The principal dissolved mineral constituents
were calcium and bicarbonate.
During periods of low flow, the chemical characteristics of the
water in the Withlacoochee River between Dade City (station 40)
and Trilby (station 42) are similar to those of the water from the
Pasco Packing Company Canal at Dade City. The source of water
in this canal is from wells penetrating the Floridan aquifer. The
mineral content of water in the canal ranged from 182 to 190 ppm.
The color of water in the canal is low (usually less than 10 units),
and the principal dissolved mineral constituents are calcium and

510 -

96 1195 61) 958 -61)
0 20 40 0 20 40 0 0 40 60 80

(o) (b) (I)
Pony Cremk Withlocooce River Wllhlocoche River
neor Polk City near Evo near Dode City

I)0 2 4 I 19- 140 1
0 20 40 60 S0 100 120 140 160

MINERAL CONTENT, IN PARTS PER MILLION
(d)

Wlthlaeochle River
at Trllby

Withlocoochee River
)a Croom

\

\

S \ "

959-01)
20 40 60 60 100 i20 140 160 IO 2

Figure 13. Relation of mineral content to discharge at gaging stations in the
Withlacoochee River basin.

Ig

0

0

-i0

-~--------- --~-~I-u~--~-Ulla~u*arsarrpa

20 40 60 80 100 120 1400 10 180 200 220 240

(f)
Little Wlthlacoochd River
at Rerdell

SO
100|T
aol

REPORT OF INVESTIGATIONS NO. 42

bicarbonate. Additional ground-water inflow in this reach of the
river is indicated. The chemical characteristics of this inflow
indicate that it was derived from the Floridan aquifer.
Gator Hole Slough, a tributary to the Withlacoochee River
downstream from Dade City, was sampled at high flow. The water
was low in mineral content and contained sodium and chloride as
the principal dissolved mineral constituents. The color was 180
units.
Data were collected during the period of low flow (May 23-25,
1961) to determine the quantity and mineral content of the
ground-water inflow in the reach of the Withlacoochee River
between the stations near Lacoochee and Trilby (see fig. 11). The
mineral content of the ground-water inflow from the Floridan
aquifer into this reach of the Withlacoochee River was computed
using the load equation (Hem, 1959):
QIC, + Q2C2 Q3C3
where, Q is the discharge in cfs
C is the mineral content in ppm
QiCi is the instantaneous load near Lacoochee
Q2C2 is the instantaneous load between data-
Collection stations
QsC3 is the instantaneous load at Trilby
The inflow (Q2) was determined to be 12.2 cfs by subtracting the
discharge near Lacoochee from that at Trilby. The mineral content
(C2) of the inflow was then computed to be 260 ppm which is
approximately equal to that of water in the Floridan aquifer in
this area.
The mineral content of water in the Withlacoochee River at
Croom (station 44) was less than that at Trilby (station 42) or
that at Rerdell (station 43). The difference between the sum of
the discharges at Trilby and Rerdell and that at Croom on May 25,
1961, was 38.9 cfs (see fig. 11). Based on the load equation, the
mineral content of the inflows between the stations would be 148
ppm. Similar computations of data during other periods show
the mineral content of the ground-water inflows in this area to
range from 148 to 174 ppm. The computed mineral content indicates
that the inflow between stations was probably a composite of
surface water and ground-water inflows.
The mineral content of the water in the Little Withlacoochee
River is shown in figure 13f. The color was usually above 100 units
during periods of high flow. The principal mineral constituents
during periods of low flow were calcium-and bicarbonate, the water

FLORIDA GEOLOGICAL SURVEY

was very hard (204 ppm), and the color was low (15 units). These
overall chemical characteristics during low flow indicate inflow
from the Floridan aquifer. The mineral content of water of the
Withlacoochee River at Croom (station 44) varied from 176 ppm
during low flow to 45 ppm during a period of high flow (fig. 13e).
The color ranged from 10 units at low flow to 120 units at high flow.
The water was soft (34 ppm) during high flow and hard (144 ppm)
during low flow.
Data collected at Lake Helene during April 1962 show that the
water was low in mineral content (51 ppm); the temperature
ranged from 760F. at the surface to 680F. at the deepest point in
the lake (25 feet); dissolved oxygen ranged from 7.5 ppm at the
top to 3.8 ppm at the bottom; and the pH ranged from 6.0 units at
the top to 5.3 units at the bottom.
The waters of Lake Mattie and Little Lake Agnes were low in
mineral content and slightly colored. These lakes are similar in
chemical characteristics to those of Lake Helene. The mineral
content of water in the three lakes is about the same as that of
water in the nonartesian aquifer.

OKLAWAHA RIVER BASIN

DESCRIPTION OF BASIN

Palatlakaha Creek is the major headwater stream of the
Oklawaha River. Figure 14 shows a flow diagram of the upper
Oklawaha River system and the names of the various segments of
the water course.
Lake Lowery, the largest of a group of lakes located near Haines
City is the headwaters of the Palatlakaha Creek basin. Most of
the drainage from Lake Lowery is to the north into Green Swamp
Run through a culvert in the old Haines City-Polk City road. At
extremely high lake stages the road is inundated.
The Palatlakaha Creek basin is confined by parallel sand ridges
that extend from Lake Lowery northward almost to Lake Louisa.
Between Lake Lowery and the Polk-Lake County line the drainage
course is called Green Swamp Run. The stream channels in this
water course are not deeply incised, and drainage is through wide
shallow swamps.
Big and Little creeks drain the basin between the Polk-Lake
County line and Lake Louisa. Big Creek is a continuation of
Green Swamp Run. The stream channels for both Big and Little

REPORT OF INVESTIGATIONS No. 42 45

creeks have more definitely incised valleys and the flood plain
swamps are not as.wide.as those for Green Swamp Run.
The Big Creek basin is confined along its eastern boundary by
the Lake Wales Ridge. However, along the boundary between Big

and Little creeks, the ridge is broken by swamps in several places
and the two basins are interconnected. Big Creek, including Green
Swamp Run, drains an area of about 70 square miles. The basin,
from Haines City to Lake Louisa, is about 25 miles long and from
2 to 4 miles wide. The swamp channel ranges in elevation from
about 130 feet near Lake Lowery to about 100 feet near Lake
Louisa.
Little Creek drains an area in Lake County west of Big Creek
and empties into Lake Louisa. The western boundary of the Little
Creek basin is fairly well defined by low ridges. However, in a few
places the ridges are broken by saddles. The exchange of surface
drainage between Little Creek and the Withlacoochee River
through the saddles in the western boundary appears to be
negligible.
The southern boundary of the Little Creek basin is not well
defined. The probable boundary is along an old road that extends
from State Highway 33 to U. S. Highway 27 about a mile or two
north of the Lake-Polk County line. Much of the drainage from
the area that was formerly drained by Little Creek has been
diverted into the Withlacoochee River by interceptor canals. These
canals are located near the Polk-Lake County line. However, some
water from its former basin still drains into Little Creek through
natural swamp channels that were not closed when the interceptor
canals were dug. The present (1962) drainage area for Little
Creek, as outlined in figure 5, is about 15 square miles during dry
periods. During wet periods, water flows into the basin through the
openings in the road along the southern boundary of Lake County.
Lake Louisa is the uppermost of a chain of large lakes in the
upper Palatlakaha Creek system. Lake Minnehaha, Lake Minneola,
and Cherry Lake are next in order below Lake Louisa. These lakes
are connected by the wide, deep channel of Palatlakaha Creek. In
addition to draining these lakes, Palatlakaha Creek also drains an
area of smaller lakes and upland marshes westward to State
Highway 33. This area affords storage facilities for large quantities
of water.
During the latter part of 1956, an earthen dam with two radial
gates was built at the outlet of Cherry Lake to maintain the stages
of the waterway and lakes upstream during prolonged periods of
dry weather. The water surface from the upper pool at this dam
to Lake Louisa is essentially level except during periods of high
discharge. During the maximum discharge period in 1960, the
stage of Lake Louisa was about 1.6 feet higher than that of the

REPORT OF INVESTIGATIONS No. 42

upper pool at Cherry Lake outlet. The fall between Lakes Louisa
and Minnehaha was 0.4 foot during this period.
The channel below Cherry Lake has been improved by a canal
leading into Lake Lucy and Lake Emma. Palatlakaha Creek follows
a more definite channel with steep gradient from Lake Emma to
its mouth at Lake Harris. The fall in this reach is about 32 feet
in 12 miles.

STREAMFLOW

Streamflow data. for gaging stations in the Palatlakaha Creek
basin during the data-collection phase of the investigation are
summarized in table 6.
The flow-duration curve for Big Creek near Clermont (station
3), adjusted from the short-term period to the 311/-year period,
1931-62, is shown in figure 15. Long-term records for the
Withlacoochee River at Trilby (station 42) were used for the
adjustment because discharges at other long-term downstream
stations on the Oklawaha River are partly regulated by
water-control structures.
Streamflow of the headwaters of the Palatlakaha Creek
upstream from Lake Louisa is unregulated. Since 1956, the flow
below Lake Louisa has been regulated by a water-control structure
at the outlet of Cherry Lake. During periods of low rainfall, most
of the drainage from the 160-square mile basin above Cherry Lake
Outlet is stored in the chain of large lakes and marshes between
Lake Louisa and Cherry Lake.
Comparison of peak discharges during floods in March 1960
and September 1960 in Big Creek, Little Creek, and the upper
Withlacoochee River shows the effect of the interconnections
between the Little Creek and the Withlacoochee River basins. The
peak discharge for the March 1960 flood in Big Creek at station 3
was 628 cfs. The discharge in Little Creek measured at station 6
near the peak of this flood was 801 cfs. The higher discharge from
the smaller drainage area of Little Creek indicates that most of the
flow was draining from the Withlacoochee basin into Little Creek
through saddles in the drainage divide.
The peak discharge during the flood of September 1960 for Big
Creek at station 3 was 691 cfs. The concurrent flood peak for Little
Creek at station 5 was 400 cfs. The flood peak for Withlacoochee
River near Eva (station 36) was 2,160 cfs in March 1960 and 1,290

TABLE 6. Streamflow

data for Palatlakaha Creek basin stations In Green Swamp area
(see figure 5 for station locations)

nRecords for part of year.
!'Maximum or minimum measured; probably
"Estimated.

not the extreme.

Runoff
in inches

Mean

112
142
12.2

1.27

'58
'51

78.4
224
251
28.7
..--

I

S3
L'

22.87
28.89
2.42

6.65
18.98
21.40
2.00

_____~_II____~ ____ ___ _________ __ _I __ ___~I_____

_~

_C~C_

REPORT OF INVESTIGATIONS NO. 42

cfs in September 1960. Little Creek serves as an outlet for much of
the flood drainage from the upper Withlacoochee River basin.

CHEMICAL CHARACTERISTICS OF SURFACE WATER

Waters of Big and Little Creeks have chemical characteristics
similar to those of the Withlacoochee River upstream from State
Highway 33 in that they have very low mineral content and are
highly colored. Figure 16a shows that the mineral content of
water in Big Creek ranges from 19 to 61 ppm. Figure 16b shows
that the mineral content of water in Little Creek ranges from 18
to 31 ppm. Color of water in Big Creek ranges from 65 to 240
units and that of Little Creek ranges from 150 to 300 units. Both
streams usually contain sodium and chloride as their principal
dissolved mineral constituents.
Waters of the two streams differ in chemical characteristics in
that water of Big Creek is more mineralized, usually less colored,
and the pH is higher than that of Little Creek. The higher mineral
content of water in Big Creek is due mostly to higher concentrations
of calcium and bicarbonate.

HILLSBOROUGH RIVER BASIN

RELATION TO GREEN SWAMP AREA

The Withlacoochee-Hillsborough overflow channel (C-9, fig. 5),
previously described with the Withlacoochee River basin, is one of
the major drainage outlets from Green Swamp during high flows
and is generally considered to be the head of the Hillsborough River.
The overflow channel as it leaves the Withlacoochee River is about
a mile wide. The road fill and bridge of U. S. Highway 98 crosses
the channel about 1 mile downstream from the Withlacoochee
River. The entire flow is confined by the road fill to the bridge
opening which is 200 feet wide.
White (1958, p.19-24) presents evidence to support an
assumption that the Withlacoochee-Hillsborough overflow channel
was formerly the main channel of the Hillsborough River and that
the Withlacoochee River was once the headwaters of the
Hillsborough River. Field studies made in the area in 1962 by
Altschuler and Meyer indicate that the Withlacoochee-Hillsborough
River overflow was formed prior to natural divergence of the

50 FLORIDA GEOLOGICAL SURVEY

headwaters of the Hillsborough River to the Withlacoochee River
and that the divergence may be related to uplift in the area.
From the bridge on U. S. Highway 98, the Hillsborough River
flows generally southwestward through Pasco and Hillsborough
counties and empties into Hillsborough Bay 531/2 miles downstream.

\\_

soI

S40

a. T2Z __- -

CUP
us

__ _
---- --

from the short-term period,
198--62, to o/-ye-ar
base period
Si I i I

11

PERCENT OF TIME INDICATED DISCHARGE WAS EQUALED OR EXCEEDED
Figure 15. Flow-duration curve for Big Creek near Clermont, 1931-62.

The lower 15 to 18 miles of the river passes through the City of
Tampa. The city water supply is a reservoir created by a dam in
the river 10.2 miles upstream from the mouth. Tampa is vulnerable
to damages from floods in the Hillsborough River because of
extensive development of property in the flood plain.

STREAMFLOW

A summary of streamflow data for the gaging station on
Withlacoochee-Hillsborough overflow (station 39) is shown in table
5. The flow-duration curve is shown in figure 10. No flow occurs
in the channel at this point about 65 per cent of the time.
Crystal Springs flows into the Hillsborough River in southern
Pasco County near the Pasco-Hillsborough County line. The average
flow of Crystal Springs (station 31) is 62 cfs, ranging from 20.3
cfs to 147 cfs. Downstream from Crystal Springs the base flow of
Hillsborough River is well sustained. The flow of Hillsborough
River near Zephyrhills (station 33), which includes flow from
Blackwater Creek, is reported to be 71 cfs or more for 90 percent
of the time (Menke, 1961, p. 29).

CHEMICAL CHARACTERISTICS OF SURFACE WATER

The chemical characteristics of water of the Hillsborough River
upstream from Crystal Springs are similar to those of the
Withlacoochee River between Eva and Dade City although the
mineral content is somewhat higher.
The water of the Hillsborough River at the Withlacoochee-
Hillsborough overflow contained calcium and bicarbonate as the
principal dissolved mineral constituents. The water contained
color that ranged from 80 to 150 units. The mineral content ranged
from 41 to 121 ppm.
The water of Crystal Springs had a mineral content of about
170 ppm, was clear, and contained calcium and bicarbonate as the
principal dissolved minerals. The water was hard and alkaline.
During the periods of low flow, the chemical characteristics of
the water of the Hillsborough River near Zephyrhills (below
Crystal Springs) are essentially the same as those of water of
Crystal Springs. Figure 17 shows the relation of the mineral
content to discharge. During periods of high flow the mineral
content of water is low. A more detailed discussion of the chemical
character of the water of the Hillsborough River is given in a
report by Menke (1961, p. 28-36).

REPORT OF INVESTIGATIONS NO. 42

5000

IL

0 0
=o
a z
2 (0

IJ
oCw
0-U_
af

Iu --

iOo
100
*
*

*

100 -- -
(1956 62)
50 ____

40 60 80 100 120 140 I1
MINERAL CONTENT, IN
PARTS PER MILLION

;0 180

200

i Figure 17. Relation of mineral content to discharge, Hillsborough River near
Zephyrhills.

KISSIMMEE RIVER BASIN

RELATION TO GREEN SWAMP AREA

The eastern boundary of the Green Swamp area is U. S.
Highway 27 atop the Lake Wales Ridge. This is generally the
surface drainage divide between Palatlakaha Creek in the St. Johns
River basin and headwater tributaries of the Kissimmee River.
The surface drainage from only 5 square miles of the Green
Swamp area flows eastward into the Kissimmee River basin.
Piezometric maps in figures 35 and 36 indicate ground-water move-
ment eastward from the Green Swamp area into the Kissimmee
River basin.

STREAMFLOW

Horse Creek is one of the Kissimmee River tributaries adjacent
to Green Swamp. Streamflow records of Horse Creek at Davenport
(station 19) were collected to study the base flow that is derived

FLORIDA GEOLOGICAL SURVEY

from ground water. The drainage area at the gaging station is
22.8 square miles. The maximum discharge during 2 years of data
collection was 358 cfs and the minimum was 0.5 cfs. Runoff
characteristics of the Horse Creek basin are compared with those
of the Pony Creek basin in a following section of this report.

CHEMICAL CHARACTERISTICS OF SURFACE WATER

Data concerning the chemical characteristics of water in the
Kissimmee River basin were collected from Horse Creek and Reedy
Creek.
Water of Horse Creek is more mineralized than water in the
upper Withlacoochee River. Figure 18 shows the general relation
of mineral content to discharge. The mineral content from July to
November 1960 ranged from 22 to 64 ppm (from daily conductivity
records). Calcium and bicarbonate were the principal dissolved
mineral constituents. The surface materials in the Horse Creek
basin are sands and clays, which are essentially insoluble in water,
and therefore the calcium bicarbonate type water in Horse Creek
is probably due to seepage from the Floridan aquifer. The following

equations were used to determine the approximate amount of
seepage from the aquifer:
Q1 + Q2 = Q
33Q1 + 167Q2 = CQ
where, Q1 is the component of discharge from nonartesian
aquifer and from direct runoff
Qs is the component of discharge from Floridan
aquifer
Q is total discharge of Horse Creek
C is mineral content of water of Horse Creek
33 is average mineral content of ppm of typical water
from nonartesian and from direct runoff
167 is average mineral content in ppm of typical water
from the Floridan aquifer.
Based on the computation, seepage from the Floridan aquifer
averaged about 6 cfs for the 4 complete months of daily conductivity
records.
Color of water in Horse Creek ranged from 60 to 160 units and
the pH ranged from 6.4 to 7.4 units.
Mineral content of water from Reedy Creek during a wet period
in 1959 was 33 ppm, the color 80 units, and the pH 6.0 units.

PEACE RIVER BASIN

RELATION TO GREEN SWAMP AREA

The Peace River basin lies immediately to the south of the
designated boundary for the Green Swamp area. Before construc-
tion of levees, highway and railroad fills, ditches and other drainage
improvements, Lake Lowery and the surrounding marsh apparently
drained southward into Peace River as well as northward to the
Palatlakaha Creek and the Withlacoochee River basins. Under
present conditions, the surface runoff from only 7 square miles of
the Green Swamp area drains southward into the Peace River basin.
This small area includes Gum Lake and its marsh outlet and Lake
Alfred. The headwaters of the Peace River basin lie immediately
south of the highest artesian water levels in the southeastern
part of the Green Swamp area. Piezometric maps in figures 35 and
36 indicate ground-water movement southward to the Peace River
basin.

FLORIDA GEOLOGICAL SURVEY

STREAMFLOW

During the flood of September 1960, caused by Hurricane Donna,
Lake Lowery reached a maximum stage of 133.32 feet above mean
sea level. During this flood, a road fill between a marsh in the
Withlacoochee River headwaters and Gum Lake marsh washed out
and an undetermined amount of water flowed southward into the
Peace River basin through an opening 12 feet wide (C-4, fig. 5).
The flow at Gum Lake marsh outlet (station 22) includes the
drainage from 4.2 square miles in the Gum Lake basin plus that
diverted from the Withlacoochee River basin through opening C-4.
During the flood of September 1960, the peak discharge was not
determined but most of this flood discharge was from the
Withlacoochee River basin. The 3' x 8' box culvert and a section
of the highway at the gaging station were overtopped. The flood
peak reached a stage of 132.0 feet above mean sea level, as
determined from high water marks at the gage. During periods
of low rainfall there is no flow in this channel. For the period May
1961 to June 1962, the channel was dry. The average discharge at
station 22 was 0.55 cfs in 1961. There was no flow from Lake Alfred
during the period April 1961 to June 1962. The total surface
outflow from the Green Swamp area to the Peace River basin is
negligible except during flood periods.

DIVERSIONS AND INTERCONNECTION OF BASINS

Although surface drainage from the Green Swamp area follows
rather definite routes and although the drainage divides are
generally determined by the topographic features, there are several
places where the basins are interconnected and water is diverted
from one basin to another. Some of these points of diversion have
been mentioned under the foregoing discussion of the individual
drainage basins. The hydrologic importance of these intercon-
nections, which are integral parts of the drainage systems, is
shown in the following discussion.
The arrows on the map in figure 5 locate and show the direction
of flow through many of the saddles in the drainage divides. The
interconnections that are shown on the map are the most important
ones disclosed by the investigation, but they by no means include
all such points in the small subbasins where there are no definite
drainage divides.
One of the major diversionary channels is the Withlacoochee-
Hillsborough overflow in southeastern Pasco County (C-9, fig. 5).

REPORT OF INVESTIGATIONS NO. 42

This diversion was discussed in detail under sections describing
the Withlacoochee River and Hillsborough River basins.
Other major interconnections of basins are near the Polk-Lake
County line (C-3) in the eastern part of the Green Swamp area.
The sand ridges in this area are dismembered by a transverse
network of swamps that connect the Withlacoochee River and Little
Creek basins. The alignment of the swamps and the relative widths
of the flood plains shown on aerial photographs indicate that, in
the former natural state, water carried to this area from the south
was discharged by either of three different routes-Big Creek,
Little Creek, or Withlacoochee River. The evidence indicates that
most of the drainage from the southeastern area ran off via Big
and Little creeks.
Beginning about 1948 and continuing progressively each year,
extensive land reclamation by property owners has considerably
altered the pattern of drainage in the eastern area. These physical
changes, which were made for the development of the area,
apparently changed the proportion of the water that drained by
the three routes. Based entirely on the present pattern of drainage
canals and without any factual data on the streamflow from the
upper basins prior to the development of the area, it appears that
the most significant change has been a decrease in the area drained
by Little Creek and an increase in the area drained by the
Withlacoochee River.
Major canals near the Polk-Lake County line were dug about
1948 and 1949 and appear to have intercepted the greater part
of the flow from an area of about 60 square miles that was formerly
the headwaters of the Little Creek basin. This area is roughly 18
miles long and 3 to 4 miles wide. It extends from the present
southern divide of the Little Creek basin southward almost to the
town of Lake Alfred. The greater part of the water from this area
now drains to the Withlacoochee River. However, as discussed in
the description of the Palatlakaha Creek basin, some flow still
enters the Little Creek basin from its former headwaters. The
changes in the drainage system predate streamflow records in the
headwater basins. Therefore, the change in proportion of drainage
between the two basins and the increased effectiveness of the
drainage system may be inferred only on the basis of long-term
streamflow records at downstream gaging stations. The runoff
under present conditions, as compared with the runoff that occurred
during the earlier years, is discussed under the heading "Effects
of Man-Made Changes" in the following section.

FLORIDA GEOLOGICAL SURVEY

A levee now fills a saddle in the drainage divide between Green
Swamp Run and the Withlacoochee River in northeastern Polk
County south of the Polk-Lake County line (fig. 5). Prior to the
construction of the levee (about 1956 or 1957), drainage from Green
Swamp Run divided into flow westward into the Little Creek basin
(now the Withlacoochee River basin) and flow northward into Big
Creek basin.
Lake Lowery and swamps in the upper Withlacoochee River
basin are connected by a natural saddle (C-1) in the confining ridge
northwest of the lake. This saddle is 200 to 300 feet wide and is
one point at which flow may be diverted between the Palatlakaha
Creek and Withlacoochee River basins. At high stages the two
basins are interconnected at this point. Apparently water may flow
through this saddle in either direction, depending on the
distribution of rainfall and the relative water levels in the basins.
There are four interconnections (C-2) between Big and Little
creeks. These openings, all in Lake County, are small and their
net exchange of water is probably negligible in comparison with the
total flow from the basin.
Other places, shown on the map in figure 5, where basins are
interconnected are: (C-4) between the Withlacoochee River
headwaters and Peace River headwaters; (C-5, C-6, C-7) between
Lake Mattie, Withlacoochee River, and Pony Creek; and (C-8)
between the Withlacoochee River and Devils Creek. Many of these
interconnections act as equalizing channels through which water
may flow in either direction, depending on relative water levels in
connected basins.

EFFECTS OF MAN-MADE CHANGES

Many of the physical changes that have been made on the land
surface through man's efforts have already been described. The
most extensive developments of the area have occurred in recent
years, but the first changes in the hydrologic characteristics
undoubtedly occurred several years ago when logging trails and
tramroads were built and much of the native timber was cleared
from the area. The early developments of the area cannot be
evaluated as they predate the period of data collection, but they
probably had only minor effects on the hydrology.
Changes in the drainage characteristics of the Green Swamp
area can be detected by comparing the hydrologic data for years
before drainage developments with the data collected since major

REPORT OF INVESTIGATIONS No. 42

developments have been made. Long-term records of rainfall and
streamflow in the upper Palatlakaha Creek (stations 11 and 12)
and Withlacoochee River (station 42) have been used to detect
changes or trends in the pattern of discharge from the upper
Palatlakaha Creek basin since 1946.
Double-mass curves of cumulative measured runoff and
cumulative computed runoff have been plotted to provide a means
of examining the records of streamflow from the area of
investigation to detect changes that may have occurred (Searcy
and Hardison, 1960). The variables used in preparing the curves
shown in figure 19 are the values of cumulative computed runoff,
taken from the precipitation-runoff relations in the figures on
pages 97 and 99 and cumulative measured runoff at each of the
two gaging stations.
The rainfall pattern is not affected by the progressive changes
in the drainage system in the Green Swamp area. The theoretical
or computed runoff based on rainfall is taken from an average curve
for several years of record. Any change in slope in the double-mass
curves of figure 19 would reflect progressive man-made changes in
runoff.
Figure 19a is the double-mass curve for the Withlacoochee
River basin above the Trilby gaging station. Straight lines are
drawn to average several points that show definite trends. These
lines change in slope between 1942 and 1943, between 1945 and
1946, and between 1953 and 1954. The two changes in slope in the
1940's indicate changes in the runoff pattern but the authors have
no knowledge of the causes of such changes. Minor deviations of
the plotted yearly values of runoff are probably caused by variations
of rainfall distribution and intensity during the year and are not
necessarily indications of changes in the long-term trends. Yearly
values of runoff for 1954-61 define an average line with less slope
than that for any previous period. This change in slope indicates
that a higher rate of runoff from the basin occurred during 1954-61
than that indicated from the same rainfall pattern of previous
years.
Figure 19b is the double-mass curve for the upper Palatlakaha
Creek basin. The figures of annual runoff were adjusted for changes
in storage in lakes. For the period 1946-49, the curve takes the
general direction .as shown by the straight line. However, after
1949, a definite break occurs in the slope of the average line
indicating, less runoff from the area.

60 FLORIDA GEOLOGICAL SURVEY

Figure 19c has been plotted to show the cumulative runoff from
the combined Withlacoochee River and Palatlakaha Creek basins.
The average line defining this curve has the same slope for the
entire period, 1946-61. This indicates that there has been no
significant change in runoff from the combined basins.

The explanation for the significant decrease in runoff from the
Palatlakaha Creek basin is a decrease in the size of the drainage
area. Such a change in the headwaters of Little Creek, a tributary
to Palatlakaha Creek, occurred during the period 1948-49 and has
been discussed earlier in this report. This change has resulted in
the diversion of part of the flow from the Little Creek basin into
the Withlacoochee River basin. The gain to the Withlacoochee
River basin is not as obvious as the loss from the Palatlakaha
Creek basin because of the difference in size of the drainage basins.

GROUND-WATER ACCRETIONS TO STREAMFLOW IN
HORSE AND PONY CREEK BASINS

Stream flow consists of direct surface runoff and ground-water
runoff or base flow. Surface runoff is rainfall that drains directly
into the stream channel during and after a storm. Ground-water
runoff is rainfall that infiltrates to the ground and then discharges
into a stream channel. In well-drained basins surface runoff ceases a
few days after the occurrence of rainfall, and streamflow is then
derived entirely from ground-water runoff. Surface contributions
to streamflow continue for longer periods in basins containing
lakes, swamps, or other surface storage features.
Daily streamflow records were collected for the period June
1960 to June 1962 for Horse Creek at Davenport (station 19) and
Pony Creek near Polk City (station 38). The runoff of these two
streams probably represents the maximum variation in runoff of
streams in the Green Swamp area. Horse Creek and Pony Creek
basins have generally similar characteristics of geology and rainfall,
but the two basins are situated differently with respect to the
piezometric high. The basin slope of Horse Creek is higher than
that of Pony Creek. Pony Creek basin above gaging station 38 is
entirely atop the piezometric high. Horse Creek above gaging
station 19 lies adjacent to the southeastern boundary of the Green
Swamp area (fig. 5) and downslope from the piezometric high
(fig. 35) in an area of artesian flow as indicated by hydrographs in
figure 23.
Graphs of monthly rainfall and runoff in inches for the Horse
and Pony creeks basins for July 1960 to June 1962 are shown in
figures 20 and 21. Base flows, expressed in inches of runoff from
the two basins, were estimated for the low runoff period from
November 1960 to June 1962. Base-flow recession curves were
developed and used as a partial basis for separation of the

Figure 21. Graphs of monthly rainfall and runoff for July 1960 to June 1962
and estimated base flows for November 1960 to June 1962, Pony Creek near
Polk City.

IU

a,
-o

-2
09_
E
w
4-5
to

I

FLORIDA GEOLOGICAL SURVEY

streamflow into the two component, base flow and direct runoff. The
methods of separating streamflow into its components of base flow
and direct runoff are hypothetical and the results are generally
subject to some limitations. During months of high runoff, July to
October 1960, streamflow was mostly from direct runoff and base
flows could not be estimated with any degree of reliability.
Monthly values of rainfall and runoff for Horse Creek and Pony
Creek are summarized in table 7. Direct runoff was computed as
the difference between total runoff and base flow. For the months
of July, August, and September 1960, the average rainfall on the
Horse Creek basin was 38.8 inches and the runoff was 13.0 inches.
For the same period, the rainfall on the Pony Creek basin was 32.1
inches and the runoff was 19.4 inches. The greater runoff from
Pony Creek resulted from less rainfall than that which occurred
in the Horse Creek basin. This was probably caused by high
ground-water levels in the Pony Creek basin and lack of storage
capacity in the nonartesian aquifer as indicated by comparison of
the hydrographs of wells in the basins (see fig. 23, well 810-136-2;
and fig. 27, well 813-149-2).
Comparison of the data for the year 1961 for the two stations
in table 7 shows that Horse Creek received 37.2 inches of rainfall
and Pony Creek received 38.4 inches. However, the runoff from
the Horse Creek basin was 6.41 inches as compared to 0.79 inch
from Pony Creek. The base flow or ground-water runoff for Horse
Creek was 4.90 inches which was 76 percent of the total runoff.
The base flow of Pony Creek was 0.40 inch which was 51 percent
of the total runoff. Most of the additional runoff for Horse Creek
in 1961 was probably gained by ground-water inflow. Base flow of
the stream was sustained even during prolonged periods of little
rainfall. On the other hand, Pony Creek basin is on top of the
piezometric high and the stream received no ground-water flow
during prolonged periods of low rainfall in 1961 and 1962.
Flow-duration curves based on the 2 years of record for Horse
Creek and Pony Creek are shown in figure 22. A comparison of the
runoff characteristics for the two basins may be made from these
curves. The curves have not been adjusted to a long-term base
period, and therefore should not be used to estimate future
long-term patterns.

AQUIFERS
Aquifers are classified as either nonartesian or artesian.
Nonartesian aquifers are unconfined, and their water surface (the

water table) is free to rise and fall. Artesian aquifers are saturated,
confined or semi-confined, and their water surface is not free to
rise and fall. The water in an artesian aquifer is under pressure
(greater than atmospheric) which causes it to rise above the top
of the aquifer. The level to which water will rise in tightly cased
wells, penetrating an artesian aquifer, is called the piezometric
surface.

The principal importance of an aquifer is its ability to transmit
and store water. The coefficients of permeability (P) and
transmissibility (T) are measures of the capacity of an aquifer to
transmit water. Permeability is usually determined by laboratory
measurements of a minute part of the aquifer, whereas transmissi-
bility usually determined in the field by aquifer tests, represents
the average permeability for a localized area of the aquifer.
The coefficient of storage (S) is a measure of the capacity of
an aquifer to store water. The coefficient of storage for artesian
aquifers is usually determined by pumping tests and may range
from about 0.00001 to 0.001. The coefficient of storage for
nonartesian aquifers can be determined by pumping tests or
laboratory methods and may range from about 0.05 to 0.30 and, for
all practical purposes, equals the specific yield.
Coefficients of permeability were determined by laboratory
analysis for samples from the nonartesian and artesian (Floridan)
aquifers in the Green Swamp area (see tables 8 and 9). Aquifer
tests were made at selected sites and the data were analyzed to
determine coefficients of transmissibility using (1) the type curve

71,8 to
72,4
209 to
260.5
282.2 to
282.5
317.5 to
817.9
447.5 to
447.9
519.5 to
510.8
1,001.9 to
1,002.5
1,169.5 to
1,169.9
1,886.8 to
1,886.6
1,476.8 to
1,477.8

1Sample fractured at end of test. Permeability may be too high.

.0006

11

121

10

.004

.02

.0001

12

.4

15

.0003

.02

Formation

S

CR

W

I

AP

AP

AP

LC

LC

0

REPORT OF INVESTIGATIONS No. 42

of the nonequilibrium formula (Theis, 1935), (2) the family of
leaky aquifer curves (Cooper, 1963), or (3) a modified
nonequilibrium formula (Jacob, 1950).
Semi-confining beds that impede the movement of ground water
comprise what is commonly called an aquiclude. Ground water will
move through an aquiclude under hydrostatic pressure. For
instance, when the water table is higher than the piezometric
surface of an artesian aquifer, the potential leakage is downward
(recharge to the artesian aquifer) and vice versa. The rate at
which ground water moves through the aquiclude depends on the
vertical permeability and the hydraulic gradient across the
aquiclude.
The aquifers of the Green Swamp area are discussed in order
of occurrence from land surface downward: (1) the nonartesian
aquifer; (2) the secondary artesian aquifer; and (3) the Floridan
aquifer.

NONARTESIAN AQUIFER

DESCRIPTION OF THE AQUIFER

The nonartesian aquifer is composed of undifferentiated plastic
deposits (table 4) which consist of fine-to-coarse-grained quartz
sand with varying amounts of kaolinitic clay.
On the eastern side of the Green Swamp area (see fig. 8, A-A'),
the aquifer ranges from about 50 to more than 100 feet in thickness.
The permeability and specific yield is higher in the vicinity of the
ridges than in the central and western areas. A relatively thin
aquiclude, consisting of clay, forms the base of the aquifer.
On the western side of the Green Swamp area, the aquifer
ranges in thickness from 0 to about 50 feet. An aquiclude consisting
of sandy clay which thickens eastward and grades into the sand of
the nonartesian aquifer forms the base.

RECHARGE AND DISCHARGE

Ground water in the nonartesian aquifer is recharged primarily
by local rainfall. It is discharged by (1) evapotranspiration, (2)
flow into streams and lakes, (3) downward leakage into the Floridan
aquifer, and (4) outflow to areas of lower head outside of the Green
Swamp area.

FLORIDA GEOLOGICAL SURVEY

Most of the nonartesian ground water in the Green Swamp area
is discharged by evapotranspiration because the water table is
relatively close to the surface and surface drainage is poor.
Evapotranspiration losses are least in the sandy ridge areas that
rim the Green Swamp because the water table is farther beneath
the ground than in the interior.
Ground water percolates downward from the nonartesian aquifer
to recharge the underlying Floridan aquifer because the water table
is usually at a higher elevation than the piezometric surface
as shown by the hydrographs in figures 23-29 and the aquiclude
(undifferentiated clay) between the aquifers is relatively thin (see
fig. 8) and permeable. The coincidence of areas of high water table
and of high piezometric head is evidence of leakage. The amount
of ground water that percolates downward is equal to the net
outflow of artesian water from the underlying Floridan aquifer.
The quantity of ground water leaving the Polk piezometric high
in the Green Swamp area, hence leakage from the nonartesian
aquifer, is presented in the table on page 116.
Nonartesian ground water moves laterally to contribute to the
surface runoff from the area. The direction of movement is
generally governed by the topography. Therefore, ground-water
divides in the nonartesian aquifer closely coincide with surface
drainage divides shown in figure 5 except along the eastern
boundary of the area where some nonartesian ground water flows
laterally beneath the Lake Wales Ridge eastward to the Kissimmee
River basin. The quantity of nonartesian ground water leaving the
Green Swamp area by lateral seepage beneath the ridge was
estimated to be insignificant in the water-budget analysis.
Fluctuations of the water table were recorded in several shallow
wells and water-table lakes in and near the southern and eastern
parts of the area, shown in figures 23-29. No data were obtained in
the western part because the nonartesian aquifer is thin or absent.
The hydrographs of wells in the nonartesian aquifer are presented
with hydrographs of wells in the secondary artesian or Floridan
aquifers to show the hydraulic relation between aquifers and the
potential movement of water in a vertical direction.
No long-term records of water-table fluctuations are available
within the Green Swamp area. However, records of water levels
in a well located southeast of the Green Swamp area (810-136-2)
show that the highest and lowest water levels since 1948 occurred
during the period of investigation.

JAN FEB MAR APR MAY JUNE JULY AUG SEPT OCT NOV DEC
1959
Figure 24. Hydrographs of water levels and rainfall at wells in the Green
Swamp area, 1959.

Water levels in most wells in the Green Swamp area show rises
in response to local daily rainfalls. Only wells 810-136-2 and
815-139-3, located in the sandy ridges east of the Green Swamp

area, show no response to local daily rainfall. Apparently, this is
due to the high retention of the thick section of sand through which
the water must percolate to reach the water table.
Hydrographs of water levels in wells located in the central
part of the Green Swamp area (figs. 27 and 28; wells 813-149-2,
i 3 129-- -- -- -

813-150-2, 814-143-2, 822-149-2, 832-154-2) show that the water
table declined less than 5 feet from a wet to a dry period (1959-62).

Figure 28. Hydrographs of water levels in wells (821-202-3; 822-149-1, 2;
832-154-1, 2) in north-central Green Swamp; in a well (826-211-1) 5 miles
north of Dade City; in wells (822-138-1, 2) 17 miles north of Haines City;
and in a well (833-137-2) 7 miles east of Clermont.

REPORT OF INVESTIGATIONS NO. 42

v^^, /

-6
130
30 .:
--8

128 Well 810-144-1
c Floridan aquifer -10

S126
12
r 124
S136
Lake Mottie

134

132
Lake Lowery
130

128 I I
J FMAMJ JASONDJ FMAMJ JASON D J FMAMJ ASOND
1960 1961 1962
Figure 29. Hydrographs of water levels in wells 810-144-1, 2 and of Lake
Lowery and Lake Mattie.
additional rainfall. Therefore, the runoff was high. Although the
hydraulic gradient between the water table and the piezometric
surface indicated that water moved downward most of the time, a
reversal in direction was noted for dry periods.
Hydrographs of water levels in wells in the southwestern part
of the Green Swamp area (fig. 25, well 805-155-1 and fig, 26, well
808-155-2) show that the water table fluctuated between 5 and 10
feet during the period 1959-62. The water table remained near the
surface during the wet years of 1959 and 1960, and the aquifer
afforded little capacity for storing: rainfall. During the dry years
of 1961 and 1962, the water table was progressively lowered by
pumping from the Floridan aquifer south of the Green Swamp.

FLORIDA GEOLOGICAL SURVEY

The area of greatest decline was in the vicinity of well 808-155-2
where the secondary artesian aquifer is absent. Large fluctuationF
of the water table in this area indicate good recharge to the
Floridan aquifer and good hydraulic connection between the
aquifers.
Hydrographs of water levels in wells east of the Green Swamp
area (figs. 23, 27, and 28, wells 810-136-2, 815-134-2, 815-139-3, and
822-138-2) show that the water table fluctuated between 5 and 10
feet during the period 1959-62. The water table occurs at depths
ranging from about 2 feet to more than 70 feet below land surface.
The area has a potentially large capacity to store rainfall. Water
moves downward from the nonartesian aquifer to the Floridan
aquifer in the Lake Wales Ridge and moves upward in the valleys
of Davenport and Reedy creeks. The best hydraulic connection
between aquifers in the eastern part of the Green Swamp area
probably occurs beneath the Lake Wales Ridge. This is indicated
by almost identical fluctuations of water levels in wells 815-139-2,
-3 (fig. 27).
Water levels in wells and sinkhole lakes, located in the
southeastern part of the Green Swamp area, fluctuated about 5
feet (fig. 29). During wet periods, the water level is near or above
land surface and water is stored in lakes and swamps. During dry
periods, water levels decline due to lack of recharge and to pumping.
Water levels in the nonartesian aquifer are generally higher than
the piezometric surface indicating recharge to the Floridan aquifer.

HYDRAULICS OF THE NONARTESIAN AQUIFER

Permeability of a 3-foot section of the nonartesian aquifer
was determined in a well (810-144-2) in southeastern Green
Swamp and in a well (815-134-2) 5 miles east of Green Swamp by
using the slug test method (Ferris, 1962). The field coefficients of
permeability for the wells were determined to be about 50 gallons
per day per square foot (gpd/ft2) and about 40 gpd/ft2,
respectively. The results of laboratory tests of disturbed sand
samples collected from a test hole in the bottom of Lake Parker
near Lakeland (Stewart, 1959) ranged from 20 to 180 gpd/ft2
(table 8). The permeability of the aquifer is probably lower in the
interior of the Green Swamp area than in the surrounding ridges
because of greater clay content.
The specific yield of the nonartesian aquifer was determined
using a graphical analysis of rainfall and water-table fluctuations

REPORT OF INVESTIGATIONS No. 42

.n wells located generally along the eastern and southern bounda-
ries and in the interior. Continuous records of water-level fluctua-
tions and rainfall were collected at each well site. The data were an-
alyzed to select short periods during which all of the rainfall was
assumed to reach the water table. One or two-day periods were se-
lected when (1) antecedent conditions compensated for moisture
requirements of the unsaturated material above the water table;
(2) the water table was far enough below the ground to store all
the rainfall and none left as runoff; and (3) the rainfall was of
short duration, high intensity, and widespread. The rise in the wa-
ter table is directly proportional to the depth of rainfall. The spe-
cific yield of the aquifer therefore is inversely proportional to the
ratio of rise in the water table in inches to the depth of rainfall in
inches.

EXPLANATION
Plots of change in water level ofter selected
5Average lope periods of rainfall recorded at same well.
Average slope =-
Specific yield 14.3% _, ----- Line represents the overage change in water level.

The specific yield of the sand comprising the nonartesian aquifer
ranged from 31.0 to 43.9 percent by laboratory analysis (table 8)
and from 12.5 to 47 percent by analysis of water-level fluctuations
caused by local rainfall, shown in figure 30.
The highest values (22.2 and 47 percent) are considered to be
representative of the aquifer in the sandy ridges that surround
the eastern and southern part of the Green Swamp area. The lower
values (12.5 and 18 percent) are considered to be representative
for the clayey sands in the central portion of the area.

CHEMICAL CHARACTERISTICS OF NONARTESIAN GROUND WATER

Water in the nonartesian aquifer in the eastern part of the
Green Swamp area is less mineralized than that in the Floridan
aquifer. The mineral content of water from the shallow wells in
this area, ranging from 30 to 50 ppm, is due to the low solubility
of the sand and clay which comprise the aquifer. The principal
dissolved mineral constituents are sodium and chloride. The iron
content ranged from 0.19 to 4.0 ppm. The 4.0 ppm in water from
well 808-139-1 was the highest found in the Green Swamp area.
The color of water from wells in the area was less than 15 units
which is lower than that of surface water.
In the western part of the area, the nonartesian aquifer is
almost nonexistent. The chemical characteristics of water in most
shallow wells and in the Floridan aquifer are similar.

SECONDARY ARTESIAN AQUIFER

RELATION TO GREEN SWAMP AREA

The secondary artesian aquifer is composed of interbedded
limestone in the undifferentiated clay (table 4). About 36 feet of
the aquifer is present in well 810-144-1 in the southern part of the
Green Swamp area. The aquifer thickens southward from the
southern boundary of the area and is an important source of
artesian water in southern Polk County. The aquifer pinches out
northward and is absent in most of the Green Swamp area.
The aquifer is recharged by downward percolation of water from
the overlying nonartesian aquifer and discharges principally by.
downward leakage to the Floridan aquifer.
Fluctuations of the piezometric surface of the secondary
artesian aquifer were recorded in well 805-155-3 (fig. 25) and the

REPORT OF INVESTIGATIONS NO. 42

surface is between the water. table of the nonartesian aquifer and
the piezometric surface of the Floridan aquifer. The clay beds
separating the aquifers are leaky as indicated by the conformance
of the fluctuations of the piezometric surfaces.

FLORIDAN AQUIFER

DESCRIPTION OF THE AQUIFER

The Floridan aquifer is the principal source of artesian ground
water in Florida. In the Green Swamp area, the aquifer is exposed
at the surface in the western and northwestern parts and occurs
at depths ranging from 50 to more than 200 feet below land surface
in the eastern part, shown in figure 31.
The Floridan aquifer is composed of marine limestones that have
been exposed to erosion and solution weathering. The formations
that comprise the aquifer in the Green Swamp area range in age
from middle Eocene to Oligocene (table 4). The Geologic cross
sections (fig. 8) show the limestone aquifer and the position of the
overlying plastic material.
The top of the aquifer is highest (90 to 100 feet above msl) in
the west-central part of the area as shown in figure 32. The base
of the aquifer was determined by the first major occurrence of
gypsum. Apparently, the gypsum fills the pores in the lower part
of the Avon Park Limestone. The existing data indicate that the
aquifer is about 1,000 feet thick in the central part of the area.
The transmissibility of the Floridan aquifer will vary depending
primarily on the occurrence of solution features such as caverns,
cavities, and pipes. The presence of dolomite in the limestone is an
indication of solution activity. Dolomite zones and cavities
generally occur in the Inglis Formation and the Avon Park
Limestone which are highly permeable. Logs of numerous wells in
the Green Swamp area indicate that a large percentage of the
cavities in the aquifer contain sand which reduces the transmissi-
bility. The low yields of some wells in the Lake Wales Ridge area
are attributed to sand-filled and clay-filled caverns.

RECHARGE AND DISCHARGE

The Floridan aquifer in the Green Swamp area is recharged by
rainfall that percolates downward from the surface of the ground
either through the nonartesian aquifer and aquiclude or directly

FLORIDA GEOLOGICAL SURVEY

into the Floridan aquifer in outcrop areas. Water is discharged
from the aquifer by (1) outflow to areas of lower piezometric head,
(2) seepage and spring flow into the streams, (3) upward leakage
to the nonartesian aquifer in areas of artesian flow, (4)
evapotranspiration, or (5) pumpage.
Piezometric maps of the area were made from water-level
measurements in about four hundred wells. These maps were
analyzed to determine areas of recharge and discharge and the
direction and rate of ground-water movement.
The first piezometric map of peninsular Florida was prepared
by Stringfield (1936) and the latest, figure 33, was prepared by
Healy (1961).
Ground water moves from high head to low head in a direction
perpendicular to the contour lines. Piezometric mounds, referred
to as "highs," usually indicate areas of recharge to the aquifer.
Piezometric depressions or troughs, referred to as "lows," usually
indicate areas of discharge from the aquifer. Recharge and
discharge may take place anywhere from the high to the low
where geologic and hydrologic conditions are favorable. Therefore,
there is no one point of recharge nor one point of discharge. The
difference in head between contour lines divided by the distance
between them is the hydraulic gradient of the piezometric surface.
The hydraulic gradient varies because of (1) unequal amounts of
recharge or discharge, (2) differences in permeability within the
aquifer, (3) differences in thickness of the aquifer, or (4) boundary
conditions within the aquifer.
Ground water in the central part of the Florida Peninsula moves
outward in all directions from an elongated piezometric high that
extends approximately from central Lake County to southern
Highlands County, generally referred to as the "Polk high," and
from a smaller piezometric high in Pasco County, commonly
referred to as the "Pasco high." The Green Swamp area occupies
a relatively small part of the Polk high. The top of the Polk high
occurs within the southeastern part of the Green Swamp area.
Ground-water drainage areas in the Floridan aquifer do not
coincide with the surface-water drainage areas in the Green Swamp,
shown in figure 34. The ground-water divides in the aquifer shift
slightly in response to recharge and discharge. Therefore, the
positions of the divides as shown in figure 34 were considered to be
average for determining the size of the ground-water drainage
areas that contribute outflow from the Green Swamp area toward
the major surface drainage areas. Water in the Floridan aquifer

REPORT OF INVESTIGATIONS NO. 42

moves generally from the southeastern part of the Green Swamp
area eastward toward the Kissimmee River Basin; westward toward
the Hillsborough and Withlacoochee River basins; southward
toward the Peace and Alafia River basins; and northward toward
the St. Johns River basin.
Figures 35 and 36 show the shape of the piezometric surface of
the Floridan aquifer in the Green Swamp area and vicinity during
a wet period (November 1959) and during a dry period (May 1962).
Analysis of the maps shows the direction of movement of ground
water did not change appreciably from wet to dry periods but the
elevations of the piezometric surface declined. The decline was
greatest along the southern and western borders and least in the
interior of the Green Swamp area. Lows or troughs in the
piezometric surface indicate that ground water discharges into
Withlacoochee River through a spring at the mouth of Gator Creek
and downstream from Dade City; into Hillsborough River at Crystal
Springs; into Blackwater Creek; into Davenport and Reedy Creeks;
and into Horse Creek. Closed depressions, such as those in the
vicinity of Lakeland, indicate the effects of pumping.
Natural hydraulic gradients, indicated by the spacing of the
contour lines in figures 35 and 36, are steep toward the Hillsborough
River on the western side of Green Swamp and toward Reedy,
Davenport, and Horse Creeks on the eastern side. The base flow
of Hillsborough River below Crystal Springs is sustained by more
than 50 cfs of ground-water inflow from the Floridan aquifer. The
base flows of streams on the eastern side of the area are sustained
by relatively small amounts of ground-water inflow from the
Floridan aquifer. Obviously then, the steep gradient toward the
east is caused by some factor other than a high rate of
ground-water discharge. The geology along the eastern side of the
Green Swamp area (see fig. 8, A-A') suggests that the steep
eastward gradient is due to a barrier, or constriction in the aquifer,
that was formed by natural grouting (sink-hole collapse and
cavity-fill) along the fractures and joints in the limestone. Thus,
the barrier effect decreases the ground-water outflow and a piezo-
metric high is formed along the eastern side.
Figure 37 shows the decline in the piezometric surface from the
wet period (1959-60) to the dry period (1962). Water levels
declined least in the interior of the Green Swamp, in the
Hillsborough River basin, and in the Kissimmee River basin
(Davenport, Horse, and Reedy-creeks). Water levels declined most
along the southern (near Lakeland), western (near Dade City),

FLORIDA GEOLOGICAL SURVEY

and northeastern boundaries. Water levels declined about 5 feet in
discharge areas (Hillsborough and Kissimmee River basins)
because the ground-water discharge is relatively uniform regardless
of seasonal variations in rainfall. Water levels declined less than 5
feet in the interior of the Green Swamp because there was little
local pumpage and the rainfall during the dry period was about
enough to balance the outflow; therefore, the aquifer remained
relatively full.
The area surrounding the Green Swamp is more populated and
developed and increased pumping during the dry period (1962)
caused a greater decline in piezometric levels than would have
occurred under natural conditions. If there had been no appreciable
increase in pumping, the map could be used to detect areal changes
in the hydraulic characteristics of the aquifer, particularly changes
in permeability.
The northernmost extent of an area of heavy pumping for
mining, industrial, municipal, and irrigational supplies is in the
vicinity of Lakeland where the water levels declined about 20 feet.
The drawdown is confined to the southern boundary of Green
Swamp, suggesting that the area of the sinkhole-riddled ridges
around southern Green Swamp is a recharge area. Water levels
declined between 10 and 20 feet on the western side of Green
Swamp in the vicinity of Dade City. This is considered to be an
area of high permeability and good recharge. Water levels declined
about 10 feet in the northeastern area which is also considered to
be an area of high permeability and good recharge.
The general conclusion is that increase in discharge (natural
or pumping) does not appreciably increase the lateral movement
of ground water from the interior of Green Swamp but does affect
the border areas.

HYDRAULICS OF THE FLORIDAN AQUIFER

Coefficients of horizontal and vertical permeability were
determined for selected core samples of the limestones that
comprise the Floridan aquifer. The samples were obtained from
well 805-154-8, located just north of Lake Parker. The laboratory
determinations are presented in table 9. The permeability values
ranged from 0.0001 to 19 gpd/ft2. The specific yields ranged from
0.2 to 23.2 percent. However, the specific yield determined in the
laboratory represents that of the rock sample and not of the aquifer
as confined.

REPORT OF INVESTIGATIONS NO. 42 83

Pumping tests were conducted in Green Swamp area and
vicinity to determine coefficients of transmissibility (T) and storage
(S) for the Floridan aquifer. The results of the tests are presented
in table 10. Values of T ranged from about 20,000 gpd/ft to about
700,000 gpd/ft. The storage coefficients ranged from 0.013 to 0.0018
which means that for 1 foot change in head of the piezometric

TABLE 10. Pumping test data (Floridan aquifer)

Aquifer Average field
Coefficient Coefficient penetration coefficient of
transmissibility Coefficient of leakage (nearest permeability
Well number gpd/ft) of storage (gpd/ft2/ft) ten feet) (gpd/ft2)

surface, the aquifer releases or takes into storage 0.013 to 0.0013
foot of water per square foot of surface area of the aquifer.
A comparison of the results of laboratory tests with pumping
tests indicate that the permeability of the Floridan aquifer is
largely dependent upon the presence of solution holes (caverns,
pipes, etc.) which, of course, are not represented in the small core
samples.

Davenport- Horse Creek area
-Eastern area
----*-- -*-- Northwestern area
a-- --- --- Southwestern area
----x---- x-- Dode City area

1 r I1 111 i iI I I i II
t---

-A
/ /

S--/ / /
I: -

SI I

0,000 100,000 1,000,000
COEFFICIENT OF TRANSMISSIBILITY
(gpd/ft)
Figure 38. Graphs showing the relations between coefficient of transmissibility
and depth of penetration in the Floridan aquifer.

The values of T for the pumping tests in table 10 were plotted
against depth of aquifer penetration, as shown in figure 38. The
wide range in values of T are caused by unequal penetration and by
areal and vertical variations in permeability. Areal analysis of
the data indicate that generally the eastern side (Davenport-
Horse Creek area) of the Green Swamp area has a low value of T
and the western side (Dade City) has a high value of T. Therefore.
the test data were evaluated by location and depth of penetration.

REPORT OF INVESTIGATIONS No. 42

The average field coefficients of permeability (Pf) table 10) were
averaged for each area and then multiplied by the approximate
thickness of the aquifer (1,000 feet) to estimate the coefficient of
transmissibility (Te) for each representative area. The data were
analyzed for (1) the Davenport-Horse Creek area east of the Lake
Wales Ridge; (2) the eastern area, which includes the general area
between State Highway 33 and U.S. Highway 27; (3) the
northwestern area, which includes the area west of State Highway
33 and north of the Withlacoochee River; (4) the southwestern
area, which includes the area west of State Highway 33 and south
of the Withlacoochee River; and (5) the Dade City area west of the
Withlacoochee River. The results of the computations (expressed
to the nearest hundred thousand gpd/ft) are presented in table 11.
Computations of ground-water movement into or out of the area
used in the water-budget analysis were based on the estimated
coefficients of transmissibility shown in table 11.

Barrier boundaries caused variations in the values of T in the
vicinity of the Lake Wales Ridge. Observation wells 815-139-2 and
815-140-1 were used to observe the effects of drawdown and
recovery caused by pumping well 814-139-5. Water level measure-
ments were also made in the pumped well. The data were analyzed
by the Theis method (1935), the family of leaky aquifer curves by
Cooper (1936), and the Jacob method (1950). The data defined
three curves, figure 39, with T values of 680,000 gpd/ft and
1,150,000 gpd/ft, for the observation wells and 120,000 gpd/ft for
the pumped well. The wide variation in T probably indicates that
the basic assumptions prerequisite for the analysis of the data do
not apply and is probably caused by heterogeneity of the aquifer
and existence of a barrier boundary. The test site is in a faulted
area (see fig. 8, C-C'). Figure 40 shows the location of the wells
with respect to sand-filled fractures in the underlying lime-
stone along the Lake Wales Ridge. The variation in T values
is probably caused by sand-filled fractures which act as barriers

Figure 39. Graphs of pumping test at a well (814-139-5)
of Haines City.

about 9 miles north

289
I.--
LI

29-
S2

o

^ 301

311L

REPORT OF INVESTIGATIONS No. 42 87

81040' 8139
28'160+g 1 EXPLANATION
Pumpf% well
Observation well
Well

n +5 Lower number is the elevation of the
zn top of the Florldon aquifer, in feet,
0 referred to mean sea level.
M -/00--
SR 5 Contour represents the approximate
o elevation of the top of the Floridon
Aquifer, in feet, referred to mean
-3 419 sea level. Contour interval 100 feet
Land surface contour, In feet, above
meon sea level. Contour interval 25 foee

2 Sand filled fractures
3 Note: structure not shown
lo0 39 I mile

Figure 40. Map showing environment affecting pumping test at a well
(814-139-5) about 9 miles north of Haines City.

between the pumped well and the two observation wells. The
barriers decrease the drawdown in the observation wells giving
erroneously high values of T. Probably the best value of T was
obtained from data from the pumped well which is comparable to
the results of a nearby test (see table 10, well 816-135-2).

CHEMICAL QUALITY OF WATER IN THE FLORIDAN AQUIFER

The quality of water in the Green Swamp area is good. The
total mineral content is generally less than 350 ppm. Water
containing a mineral content of less than 500 ppm is usable for most
purposes. The water of the Floridan aquifer is more mineralized
(100-400 ppm) than surface water or water from the nonartesian
aquifer (20-50 ppm). The higher mineral content is caused by
contact of water with materials that are more soluble. About 75
percent (by weight) of the mineral constituents dissolved in water
of the Floridan aquifer are calcium and bicarbonate that cause the
water to be hard and alkaline. Hardness, illustrated in figure 41,
is one of the more undesirable characteristics. The water ranges
from moderately hard in the eastern part of Green Swamp to very
hard in the western part.
Figure 42 shows the iron content of water in the Floridan
aquifer in the Green Swamp area. The highest concentrations of

FLORIDA GEOLOGICAL SURVEY

iron are found in the west-central part of the area. Iron greater
than 0.20 ppm generally should be removed for most uses.
Other dissolved mineral constituents, including silica, potassium,
sulfate, and chloride, occur in concentrations generally less thail
10 ppm. Fluoride and nitrate are usually present in concentrations
less than 1.0 ppm. The water is clear (color less than 5 units), the
temperature ranges from 74 to 780F., and the pH ranges from 6.8
to 8.6 units.
Water from a well (830-210-2) near the northwestern boundary
had a sulfate concentration of 101 ppm. The high sulfate
concentration is due to contact of water with gypsum. Samples of

Figure 41. Hardness of water in the Floridan aquifer in the Green Swaml
area.

REPORT OF INVESTIGATIONS NO. 42

Figure 42. Iron content of water in the Floridan aquifer in Green Swamp
area.
a well (810-144-1) located on the piezometric high were analyzed
for trace elements, none of which were present in a concentration
that would impair the usability for most purposes.

HYDROCHEMISTRY OF THE FLORIDAN AQUIFER IN
CENTRAL FLORIDA
The chemistry of water in the Floridan aquifer can be used to
gain a better understanding of the hydrology of the Green Swamp
area and the recharge potential of the Green Swamp as compared
to the rest of the central Florida area. The chemistry of the water

FLORIDA GEOLOGICAL SURVEY

in an aquifer depends on the chemical character of the water
entering the aquifer, the chemical character of the rocks and water
in the aquifer, and the time the water entering the aquifer is in
contact with these rocks and water.
Water entering the aquifer in the Green Swamp area and in
central Florida in general, is less mineralized than water already
in the aquifer. Water is low in mineral content because the
overlying sands and clays generally are less soluble than the
limestone of the Floridan aquifer. Therefore, in recharge areas the
mineral content should be lowest, other factors being equal. The
mineral content of the water should increase as the water moves
through the aquifer until it becomes saturated with calcium and
bicarbonate. Using only the mineral content to indicate areas of
recharge could be misleading because water entering the aquifer
in some areas could be more highly charged with carbon dioxide
than in other areas. High amounts of carbon dioxide in water
dissolves more limestone than small amounts. In some coastal
areas, the water in the aquifer already contains high concentrations
of salt.
The percentage of limestone that was dissolved by the water
in the aquifer in central Florida was calculated from measurements
of alkalinity, pH, temperature, and mineral content (Back, 1963)
and is shown in figure 43. Saturation values less than 100 percent
indicate that the water could dissolve more limestone. Values of
more than 100 percent indicate that the water is oversaturated and
would therefore tend to precipitate limestone. Figure 43 shows
undersaturated water occurs in the aquifer along the eastern and
western boundaries of the Green Swamp and to the north. Water
in recharge areas should be undersaturated and the percent of
saturation should increase as the water moves away from the
recharge area (Hem, 1961, p. C-15). If the recharge occurs only in
the Green Swamp area, then the saturation values should be lowest
in this area and should increase in all directions from the area.
Figure 43 shows that the area of undersaturation includes much
of central Florida and thus implies that recharge occurs over much
of this area.
In the areas of undersaturation, caverns or fissures can be
enlarged by limestone solution several hundred feet below the water
table (Back, 1963). High rates of water movement through these
caverns and fissures could account for the occurrence of
undersaturated water at these depths. The time and area of contact
of water with the limestone in these openings would be minimized.

Figure 43. Map of central Florida showing the percentage of calcium
carbonate saturation of water in the Floridan aquifer.

FLORIDA GEOLOGICAL SURVEY

The presence of highly mineralized water in the Floridan
aquifer may also be used to indicate the direction of movement of
water. Assuming that at some time much of the aquifer of central
Florida contained salt water, then the area in which the water now
contains little or no salt (chloride), would be better flushed with
fresh water than areas containing high amounts. The chloride con-
tent is generally higher at shallow depths near the coast than in the
interior, shown in figure 44. However, water of low chloride content
is present several hundred feet deep in local areas near the coast.
Data from a few scattered deep wells indicate that fresh water
extends to about 1,500 feet below sea level in much of the interior
of central Florida from Marion County to Highlands County.
Figure 44 and other data from the deep wells indicate that salt
water has been flushed from the aquifer in much of the interior.
Therefore, the total mineral content of the water in the Floridan
aquifer in the interior of Florida is due to solution of limestone
and not due to mixing with salt water. If recharge occurred only
in the Green Swamp area, then the concentration gradient should
increase in all directions from that area. Figure 45 shows that
the concentration gradients do not increase immediately away from
the Green Swamp but instead show a decrease over much of central
Florida. The areas of low mineral content and areas of under-
saturation generally coincide (figs. 43 and 45). This supports the
implication that recharge is not confined to the Green Swamp area.

ANALYSIS OF THE HYDROLOGIC SYSTEM

The Green Swamp area is considered to be a self-sustaining
hydrologic unit because most of its water supply is derived from
rain that falls directly on the area. Water is imported from outside
the area only in the vicinity of Dade City (see figs. 5, 11, 35, 36).
Inflows in the vicinity of Dade City affect only the lower reaches
of the Withlacoochee River.
The amounts of water in the various parts of the hydrologic
system and losses of water as the result of natural processes, are
evaluated for the Green Swamp area.

RAINFALL, RUNOFF, AND WATER LOSS

Runoff is the residual of precipitation after all the demands of
nature have been met. These demands taken collectively are called
water loss. A simple definition for water loss is: Water loss equals
precipitation minus runoff adjusted for change in storage and for

Figure 44. Vertical distribution of chloride content of water in wells across
central Florida.

26o -

3000-
OOO-

3200-

3400-

3600-

3800-

FLORIDA GEOLOGICAL SURVEY

v o:I i

II \

c:" Do --. \

NI Sai. ]Com t'r i ofII uequl
0his

Figure -5. Map of central Florida showing mineral content of water in the
Floridan aquifer.

seepage into and out of the basin. The basic concept is that water
loss is equal to evapotranspiration; that is, water that returns to
the atmosphere and thus is no longer available for use. As used in
this report, water loss is not adjusted for seepage into or out of

where, L is water loss
P, is effective precipitation
i I

R is streamflow
AS is change in storage both

surface and underground
Use of an effective precipitation (Searcy and Hardison, 1960)
is one way5. ap of makicentrallorida showing mineral contee amount of water in the
Floridan aquifer.

seepage into and out of the basin. The basic concept is that water

carrloss is equal to evapotranspiration; that is, water that returns tobasin.
the atmosphere and thus is no longer available for use. As used in
this report, water loss is not adjusted for seepage into or out of
the basin. Thus, the equation for water loss is:

where, L is water loss

Sis effective precipitation (P), as commonly used, is that part of the
precipitation (Po) for the current year and the part of the
AS is change in storage both
surface and underground

Use of an effective precipitation (Searcy and Hardison, 1960)
is one way of making allowance for the variable amount of water
carried over from year to year as ground water storage in the basin.
Effective precipitation (Pe), as commonly used, is that part of the
precipitation (P0) for the current year and the part of the

REPORT OF INVESTIGATIONS No. 42

precipitation (P,) for the preceding year that furnished the runoff
for the current year, or

Po = aPo + bP,
The coefficients a and b are determined by statistical correlation.
Long-term annual records of rainfall and runoff for the
Withlacoochee River and Palatlakaha Creek basins have been used
to determine the variations in water loss in the Green Swamp area.
Areal variations in water loss are caused by: (1) climatic factors,
the most important of which are rainfall, temperature, humidity,
and wind; (2) drainage basin characteristics, which include size,
shape, surface slope, the amount of water area, seepage as related
to the surface and sub-surface geology, and the condition and type
of vegetative cover; and (3) storage underground and in natural
lakes, ponds, swamps, and artificial reservoirs. The effective annual
precipitation determined for the Withlacoochee River basin above
Trilby and for the Palatlakaha Creek basin above Mascotte is

P, = 0.8P,, + 0.2P,
The annual water-loss curve for Withlacoochee River at Trilby
is shown in- figure 46. The Po = L line (dashed line) in figure 46
represents the theoretical limit of water loss which would occur if
the loss equaled the precipitation and none ran off as streamflow.
The average water-loss curve is shown by the solid line which was
drawn to average the annual figures of effective precipitation and
loss (P, R) for the basin. The departures of the yearly data
from the average curve may be caused in part by changes in
storage and seepage and in part by differences in the distribution
of precipitation within the year. No adjustment is made for these
factors in the water-loss equation for Withlacoochee River at Trilby
and they thus affect the apparent evapotranspiration.
An effective annual precipitation of about 32 inches, indicated
by the point where the downward extension of the curve coincides
with the Po = L relation, is the most probable yearly amount below
which little significant runoff would occur. Under some conditions
of intensity and distribution of precipitation, there could be runoff
with less than 32 inches of precipitation.
As shown by the curve in figure 46, the average water loss
increases with the precipitation until it becomes nearly a constant
for higher values of precipitation. This is about the maximum loss
that would occur regardless of the amount of precipitation and is
called the potential natural water loss for the basin. The potential

natural water loss for the Withlacoochee River at Trilby is shown
to be 45 inches. This figure compares favorably with the 48 inches
of average water loss shown for 720F., the mean annual
temperature for the area, in figure 7.
Figure 47 shows the plotted yearly figures of rainfall and
runoff for the Trilby station and an average curve. The average
cu;ve was determined by using the curve in figure 46 and plotting
the departures of the potential water-loss curve from the limiting
curve(P. = L).

The runoff from the upper Palatakaha Creek basin has been
measured since 1945 (stations 11 and 12 in table 1). The water-loss
curve for the upper Palatlakaha Creek basin is shown in figure 48.
Runoff was adjusted for annual changes in storage in the many
lakes and swamps in the basin. No allowance was made for change
in underground storage or for seepage into or out of the basin.
The water-loss curves shown in figures 46 and 48 indicate that,
for a year in which rainfall was 32 inches or less, the natural losses
would nearly equal the rainfall and little or no runoff would occur
from either the Withlacoochee River or the Palatlakaha Creek
basins in the Green Swamp area.
As shown in figure 48, the potential natural water loss for the
upper Palatlakaha Creek basin is 48 inches which is the same as the
annual water loss shown for 72F. in figure 7. Figure 49 shows the
t

80

70 ---- --------------------- ---- --__----- -3------

60

50

-3--
*/"

40 *
Note Total runoff adjusted
to include diversions
above station into
Hillsborough River
30

30 ----------- --- ----

0

FLORIDA GEOLOGICAL SURVEY

relation of the effective annual rainfall and runoff for the upper
Palatlakaha Creek basin.
The potential natural water loss, indicated by this analysis for
each basin, includes both evapotranspiration and ground-water
outflow. Further analyses show that about 2 inches more ground

water flows from eastern basins than from western basins (table
14). The gain in streamflow by ground-water pumpage at Dade
City reduces the apparent water loss in the Withlacoochee River
basin above Trilby. The many large lakes and swamps in the upper
Palatlakaha Creek basin afford the opportunity for high evapo-
transpiration losses. The differences in ground-water inflows and
outflows in the Palatlakaha Creek and Withlacoochee River basins
and the increased evapotranspiration losses from the large lakes
and swamps could easily account for the 3 inches more potential
natural loss from the Palatlakaha Creek basin.

WATER-BUDGET STUDIES

A water budget is a quantitive statement of the balance between
the total water gains and losses of a basin or area for a period of
time. The budget considers all waters, surface and subsurface,
entering and leaving or stored within a basin. Water entering a

FLORIDA GEOLOGICAL SURVEY

basin is equated to that leaving the basin, plus or minus changes in
basin storage.
The budget equation was the basis of the expression for
determining the water-loss equation in the foregoing discussion of
rainfall, runoff, and water loss. The water-budget equation may be
expressed in greater detail as

P = R + ET + U + AS, + SS
where: P is precipitation
R is streamflow
ET is evapotranspiration
U is ground-water outflow
AS, is change in surface-water storage
(+ for net gain; for net loss)
AS, is change in ground-water storage
(+ for net gain; for net loss)
Precipitation (P) and streamflow (R) are factors of the budget
equation that can be measured directly. The other factors are not
measured directly but are derived from observed or deduced data.
Ground-water outflow (U) in the Green Swamp area is the net
amount of water that moves out of the basin by subsurface flow
through both the nonartesian and Floridan aquifers.
The amount of water leaving the nonartesian aquifer by
horizontal underflow is an insignificant factor in the budget where
the water-table divides coincide with the surface-water divides. In
the Green Swamp area, the divides on the eastern boundary do not
coincide and a small quantity of water leaves the area via the
nonartesian aquifer.
The amount of water leaving the area via the Floridan aquifer
was estimated by using the hydraulic coefficients of the aquifer
and piezometric maps.
The gain or loss of water by storage changes (AS, and ASg) in
an area such as the Green Swamp may be a significant quantity for
short periods. However, by using selected long-term periods, the
effects of storage changes are minimized. The change in surface-
water storage (AS,) is indicated by change in stage of lakes, stream
channels, and swamps in a basin. In this analysis, the open water
surfaces were considered to be a small percentage of the total
drainage area, and estimates for storage changes in the nonartesian
aquifer were used for an overall storage change including AS,.
The change in ground-water storage (AS,) is the net change in
ground-water stage multiplied by the specific yield for (or storage

100

REPORT OF INVESTIGATIONS No. 42

coefficient) of the aquifer for a given period of time. Separate
analyses were made for both the nonartesian and the Floridan
aquifers.
Evapotranspiration (ET) cannot be measured directly for
large areas such as the Green Swamp, but may be approximated
by balancing the water-budget equation and determining the
residual quantity. The other quantities of water loss are small in
proportion to the quantity lost by evapotranspiration. Therefore,
the residual quantity in the equation reasonably represents the
evapotranspiration loss.

EVAPORATION AND WATER BUDGET OF LAKE HELENE
Most of the precipitation that falls on an area is dissipated
through the natural processes of evaporation and transpiration.
Because evaporation plays such an important role in the hydrologic
cycle, much effort was expended to measure it directly at Lake
Helene instead of calculating it as a residual in the storage equation.
Harbeck (1962) describes a practical method for measuring the
evaporation from an open-water surface utilizing the mass-transfer
theory. A report by the U. S. Geological Survey (1954), and one
by Harbeck and others (1958), may be consulted for additional
information on the method.
The mass-transfer method provides a technique for measuring
the evaporation and for determining the seepage from a lake, two
factors of the water budget that are generally determined indirectly
or estimated. The change in volume resulting from evaporation
on the water surface of a lake is computed by use of an empirical
equation based on measurements of the evaporative capacity of the
air. The water-budget equation is then balanced to account for
volume changes from rainfall, surface inflow and outflow,
evaporation, seepage, and other consumptive losses.
Evaporation computed by applying a coefficient to measured
evaporation from a pan may be subject to considerable error,
particularly for periods of less than a year. The annual average
Class-A pan coefficient for central Florida has been estimated by
Kohler and others (1959, pl. 3) to be about 77 percent. The monthly
evaporation-pan coefficients vary more widely and with a greater
range of probable error than the annual coefficients. There is,
therefore, the need to supplement pan records with direct
measurements of evaporation.
Evaporation from Lake Helene was measured in 1962 by use
of the mass-transfer method. Lake Helene is located about 1 mile

101

FLORIDA GEOLOGICAL SURVEY

southeast of Polk City on top of the piezometric high (see figs. 5 and
35). The lake has no surface inlet and no surface outlet except at
extremely high stages, and in 1962 its surface area ranged from
56.6 to 51.2 acres. It is nearly devoid of vegetative growth;
consequently, transpiration losses are negligible. A map of Lake
Helene showing depth contours is given in figure 50. The depth-
contour map for Lake Helene is taken from a report by Kenner
(1964): This map shows the locations of the water-stage and
rainfall recorder and the raft in mid-lake supporting an anemometer
and a water-surface temperature recorder.
Figure 51 is the hydrograph of the daily stage of Lake Helene
from March 31, 1961, to December 31, 1962. The evaporation
station was established December 13, 1961. Computations of the
evaporation data for the 1962 calendar year have been summarized
and used to help define the annual water budget.
Pumpage of water from Lake Helene to irrigate the surrounding
citrus groves contributes to water loss from the lake. A pumping
station capable of pumping 1,800 gallons per minute was installed
in 1962 and operated intermittently during the year. The volume
changes due to pumpage from the lake were computed from the
recorded changes in stage and stage-volume relations. These
computations were verified by records of the approximate periods
of pumpage and the rated capacity of the pump.
Nearly all the gains of water in the lake were derived from
rain that fell directly on the water surface. The lake stage increased
approximately the same amount as the recorded depths of rainfall
during light to moderate rain storms. However, during a few heavy
rain storms the lake stage increased slightly more than the depth
of rain, indicating runoff from land. The increase in lake stage
during these periods is equivalent to the total gain for rain falling
directly on the lake and from runoff. Net seepage to or from the
lake caused a gain in volume at times and a loss at other times.
The water-budget equation for Lake Helene may be expressed
as follows:
V = P + R +Se- E-Pu
where:
AV is change in lake volume
(+ for increase; for decrease)
P is precipitation on lake
R is runoff from land
Se is seepage
(+for net gain; for net loss)

E is evaporation from lake
Pu is pumpage from lake
The monthly water budget for Lake Helene for 1962 is shown in
table 12. The total loss from evaporation was 53.10 inches as shown
in column 12. Seepage to or from the lake was variable as shown
by the monthly amounts in columns 10 and 11. Net seepage for the
year was 6.64 inches from the lake.
The items of inflow and of outflow for Lake Helene were
determined independently. Computed values of change in volume
(column 16) are the algebraic sums of the items of inflow and items
of outflow for each month. These values compare closely with the
observed values of change in storage shown in column 17.
Average annual lake evaporation in this part of central Florida
for a 10-year period (1946-55) has been estimated to be about 49
inches (Kohler and others, 1959, pl. 2). Evaporation losses from
Lake Helene for 1962 exceeded Kohler's estimate, based on a
10-year average, by about 4 inches. Records from several
evaporation pan stations show that evaporation amounts are
generally higher during dry years. Thus, the measured evaporation
from Lake Helene during 1962, a dry year, may be higher than for
an average year.

COMPARISON OF EASTERN AND WESTERN BASINS

Geology and topography, the two predominant factors affecting
the water budget of the Green Swamp area, are somewhat different
in the eastern and in the western parts of the area. The effects of
these factors on the components of the water budgets have been
determined by the selection of representative basins in each part
for defining the budget equation.
The drainage basins east of State Highway 33 are intercon-
nected by swamp channels (see fig. 5) and flood runoff from each
basin may not be representative of that originating within the
basin. However, the sum of the discharges measured at Big Creek
at station 3, Little Creek at station 5, and Withlacoochee River at
station 36 represents approximately the natural streamflow from
the combined drainage basin of 208 square miles. Small amounts
of water may be exchanged with other basins at interconnecting
points designated as C-4, C-5, C-6, and C-7 in figure 5. The amount
and duration of flow through these openings are considered to be
insignificant in comparison with the total amounts measured at
the three gaging stations. In the following analysis of the water

budget the combined basins east of State Highway 33 are referred
to as eastern basins.
Runoff of the Little Withlacoochee River at Rerdell (station
43) is representative of the natural drainage in the western part
of the Green Swamp area. Streamflow at the gaging station is
derived from rainfall on the Little Withlacoochee River basin. The
drainage area at station 43 is 160 square miles.
Water budget analyses were made for the eastern and western
basins. Figure 52 shows the daily streamflow from these basins
for the calendar years 1959-61. Streamflows, ground-water levels,
and lake levels were nearly the same at the beginning and end of
the year both in 1959 and 1960. Although these were the 2 wettest
years of at least 60 years of record in central Florida, the indicated
year-end storage changes were small and insignificant.
The year 1961 was one of the driest of record, and the annual
runoff was low. Stream discharges were less and water levels, as
indicated at representative ground-water observation wells and
lake gages, were generally 1 to 3 feet lower at the end of 1961 than
at the beginning. The surface runoff from the eastern basins in
1961 was 1.7 inches and that from the Little Withlacoochee River
basin was 0.8 inch.
Ground-water outflow from the Floridan aquifer in the eastern
and western basins was computed using the piezometric maps
(figs. 35 and 36). The piezometric surfaces shown by the map
for November 1959 (fig. 35) and the map for May 1962 (fig. 36)
represent the flow conditions and the probable range in the rates
of ground-water movement during wet and dry periods, respec-
tively. The piezometric surface representing flow conditions for
the year 1961 was assumed to be the average between that
shown by maps for November 1959 and May 1962.
The western part of the Green Swamp area, as represented by
the Little Withlacoochee River Basin received more rainfall each
of the 3 years than did the eastern part of the area. Runoff from
the eastern basins was almost as much as that from the Little
Withlacoochee River basin in 1959 and 1960 even though the
rainfall was 3.4 inches less in 1959 and 5.6 inches less in 1960. In
1961, a dry year, 0.9 inch more runoff occurred from the eastern
basins than that from the Little Withlacoochee River basin
although the yearly rainfall was 0.9 inch less.
Where and when the ground-water and surface-water divides
coincide, some ground water from the nonartesian aquifer
discharges from a basin as the base flow of the stream draining

I -- I I~ 'e_ --p ~

107

FLORIDA GEOLOGICAL SURVEY

the basin. The divides do not coincide along the eastern boundary
of the Green Swamp area because little or no water reaches the
water table beneath the ridge. During dry periods, the water-table
divide is located about 3 miles west of U. S. Highway 27, and
nonartesian ground water moves laterally beneath the Lake Wales
Ridge from the St. Johns River basin to the Kissimmee River basin.
During seasonally wet periods, however, there is sufficient
downward seepage through the ridge sediments to build up a
temporary ground-water divide beneath the Lake Wales Ridge.
This low wet-season divide recedes rapidly and the hydraulic
gradient is resumed from the Green Swamp eastward to the chain
of lakes, swamps, and streams which lie at the base of the eastern
side of the Lake Wales Ridge. Ground water moves eastward in
the nonartesian aquifer beneath the ridge along a 25-mile stretch
from Haines City almost to Clermont. Data from wells drilled on
each side of the ridge indicate that the nonartesian aquifer is about
100 feet thick. Hydraulic gradients to the east in the nonartesian
aquifer, measured across the ridge at 10 locations, averaged 6.6
feet per mile. The coefficient of permeability of the nonartesian
aquifer beneath the ridge probably ranges from 20 to 180 gpd/ft2
on the basis of data shown in table 8. Using an assumed coefficient
of 200 gpd ft.', the computed ground-water discharge from the
nonartesian aquifer in the eastern area was about 5 cfs in 1961.
This discharge from the 208 square-mile area is equivalent to 0.3
inch, an insignificant budget factor.
The ground-water outflow from the basins through the Floridan
aquifer was computed as follows: (1) the drainage basin map
(fig. 5) was overlain by the piezometric maps and streamlines were
drawn to intersect and subdivide the boundary of each selected
basin into numerous flow sections, shown in figure 53; (2) the
hydraulic gradient (I), computed from the map, was multiplied by
the length of the flow section, also scaled from the map, to obtain
a flow factor for each flow section; (3) the discharge through each
section was computed by multiplying the flow factor by the
coefficient of transmissibility; (4) the sum of discharges through
all flow sections around the boundary represents the net ground-
water discharge from the basin. The total discharge was computed
in units of million gallons per day (mgd) and converted to cubic
feet per second (cfs); (5) ground-water discharge from a drainage
basin was expressed in terms of outflow in inches for the basin so
that it could be compared readily with rainfall and surface runoff.

108

REPORT OF INVESTIGATIONS NO. 42

The net ground-water outflow (U) thus computed from the
Floridan aquifer for the.eastern and western basins for November
1959 and May 1962 are presented in table 13. About 80 percent
of the outflow from the western area originated from rainfall
within the basin; the remaining 20 percent was inflow from the
eastern basin. All outflow from the eastern area originated from
rainfall within the basin. More than half of the total amount of
ground water leaving the eastern basin flows to the Kissimmee
River basin. The mean annual ground-water outflows from the
eastern and western basins for the years 1959 and 1960 are assumed
to be the same as those shown in table 13 for November 1959.
The mean annual values for 1961 are assumed to be averages
between the values for the two periods in table 13. Mean annual
ground-water outflows thus computed for the 3 years are
summarized in table 14.
Annual changes in the amount of ground water in storage in
the nonartesian aquifer were determined for the period 1959-61.
The net change in storage for the years 1959 and 1960 is negligible.
However, the net loss in water from storage during 1961 amounted
to about 7.4 inches in the eastern basin and about 2 inches in the
western basin. These storage losses add to precipitation as a source
of supply in the water-budget equation.
Coefficients of storage of the artesian Floridan aquifer are
small (table 10). Therefore, changes in ground-water storage
during the period 1959-60 were insignificant quantities. During
1961, the net decrease of the piezometric surface was about 2 feet,
which is equivalent to a loss of about 0.2 inch of water from the
basins. This is an insignificant budget factor. Thus, change in
storage shown in table 14 was computed for only the nonartesian
aquifer.
Comparative results of the annual water-budget for the eastern
and western basins are summarized in table 14.

OUTFLOW FROM GREEN SWAMP AREA
The total surface runoff from 818 square miles, which includes
most (94 percent) of the Green Swamp area, was measured at each
of the five major outlets. Listed in table 15 are the mean monthly
discharges determined at each of these outlets from the beginning
of the investigation in July 1958 to June 1962.
Table 15 shows the distribution of total discharge from month
to month as well as that from the individual streams draining from
the area. The effects of wet and dry years on the amount and

109

Ir"
O

TABLE 13. Ground-water outflow from the Floridan aquifer for eastern and western basins

*Estimated on basis of discharge measurements at monthly intervals and records for other stations.

FLORIDA GEOLOGICAL SURVEY

Stream line ( indicates
direction of flow)

L. FLOW SECTION No. I

\

I. Flow factor = I x L
ft
Where I is the hydraulic gradient (-'-)
100-90 foot contours
d (miles)
and L is the length of the section in miles
2. Flow section
Discharge (gpd)= Flow factor x Coefficient of transmissibility

Figure 53. Sketch showing analysis of a flow section.

distribution of runoff from the area. are shown in this table. The
years 1959 and 1960 were the wettest of record and 1961 and 1962
were the driest.
The discharges given in table 15 indicate that Little Creek and
Withlacoochee-Hillsborough overflow carry significant amounts of
water from the area only in wet years. During 1961, Little Creek
carried only 0.9 percent and the Withlacoochee-Hillsborough
overflow carried only 0.2 percent of the total surface outflow from
the area. Both channels were dry during most months in 1961 and
1962.
Ground-water outflow (U) from the Polk high was also
computed using the flow net method of analysis of the piezometric

114

REPORT OF INVESTIGATIONS NO. 42

surfaces of November 1959 (fig. 35) and May 1962 (fig. 36). These
computations exclude the ground-water inflow from the Pasco high
to the Green Swamp area in the vicinity of Dade City.
Outflows from each major basin were computed using ground-
water areas enclosed by the divides as shown in figure 34. The
distribution of the outflows from the Polk high to the major
drainage basins is shown in table 16.
Most of the natural outflow is contributed to the Kissimmee and
Withlacoochee River basins. Increased pumping for mining,
irrigation, and municipal supplies in the southern part of the area
(from Lakeland to Haines City) during the dry period caused about
50 percent increase in outflow to the Peace and Alafia River basins.
Significant changes in outflow in the dry period also were
experienced in the Withlacoochee and St. Johns River basins. The
decrease in outflow to the Kissimmee River basin and the
corresponding increase to the Peace River Basin were caused by
slight shifting of the ground-water divides. The ground-water
outflow in 1959 is considered to be more representative of natural
outflow.
Net ground-water outflow (U) from the Green Swamp area was
computed using the same method as used for the eastern and
western areas. The total outflow via the nonartesian aquifer was
determined to be an insignificant quantity (0.08 inch per year).
The total outflow via the Floridan aquifer was computed along the
boundary of the 870 square-mile area.
The net ground-water outflow from the Floridan aquifer during
November 1959 and May 1962, adjusted to equivalent amounts of
runoff in inches per year, are presented in table 17. The estimated
mean annual ground-water outflows interpolated for 1959, 1960, and
1961, on the basis of yearly totals in table 17, are presented in
table 18.
The net change in ground-water storage in both the nonartesian
and Floridan aquifers for 1959 and 1960 are considered to be
negligible. However, water levels in both aquifers declined
significantly in 1961. The average net decline of water levels in
the nonartesian aquifer in 1961 was equivalent to about 4.3 inches
of water over the Green Swamp area. The average net decline of
the piezometric surface of the Floridan aquifer in 1961 was
equivalent to an insignificant change in storage (0.2 to 0.3 inch)
because of artesian storage coefficients.
Rainfall, surface-water outflow (table 15), ground-water outflow
(table 17), and changes in ground-water storage are combined in

115

TABLE 16, Ground-water outflow from the Polk plezometric high in Green Swamp area

Basin receiving
ground-water
drainage from
Green Swamp area

St. Johns River
(Palatlakaha Creek)
Kissimmee River
Peace River
Alafl'a River
Hillsborough River
Withlacoochee River
(excluding 45 sq. mi.
area in vicinity of
Dade City)

Total

the
N
Ground-water a period
contributing Coefficient of
area transmissibility
(sq. mi.) (gpd/ft) (mgd)

sOutflow from
the Floridan aquifer,
May 1062,
a period of low water levels
,,eren

(mgd) (eta) of total

167.0

88.2
89.7
80.7
60.6
23.8
15.2
81.4

258.8

Assuming that the computed outflow is the mean annual discharge:
Ground-water for a wet year would be 8.0 inches.
Ground-water outflow for a dry year would be 4.2 inches.
&Increased outflow during dry period due to increased pumping near the boundaries.

TABLE 17. Ground-water Qutflow from Green Swamp area

Outflow from bOutflow from
the Floridan aquifer, the Floridan aquifer,
November 1959, May 1962
Basin receiving Ground-water a period of high water levels a period of low water levels
ground-water contributing Coefficient of
drainage from area transmissibility Inches I Inches
Green Swamp area (sq mi) (gpd/ft) (mgd) (cfs) per year (mgd) (cfs) per year

*Assuming computed outflow is mean annual discharge.
bIncreased outflow during dry period due to increased pumping near the boundaries.
CTransmissibility of 500,000 gpd/ft used east of Withlacoochee River and 1,200,000 used west.
dNet minus outflow is result of greater inflow from Pasco high.

0 '

0
-4

02

FLORIDA GEOLOGICAL SURVEY

the water-budget analysis of the Green Swamp area for the period
1959-61. Yearly summaries of the budget factors are presented in
table 18.
Surface runoff is directly dependent on rainfall and varies
through a wide range as shown by comparison of the wet years of
1959 and 1960 with the dry year of 1961. On the other hand, the
ground-water outflow from the area varied little from the wet to
dry years. Though the difference is small, the ground-water outflow
was more during the dry year than during either wet year. The
increase in ground-water outflow during 1961 was caused primarily
by increased pumpage from the Floridan aquifer in the area along
the southern and western boundaries of the Green Swamp area.
The net loss in ground-water storage during 1961 also was greatest
along the boundaries reflecting the drawdown effects caused by the
pumpage.
The 3-year average evapotranspiration loss was 36.8 inches from
the Green Swamp area as shown in table 18. Evaporation from
Lake Helene in 1962 amounted to 53.1 inches (table 12). Compari-
son of these values indicates that exposure of the water surface by
impoundment in reservoirs would increase the evaporation loss by
about 16 inches per year per unit area in the Green Swamp. Other
studies indicate that the increased evaporation loss would be less
than 16 inches. Estimates by Kohler and others (1959) indicate
that the average annual lake evaporation in central Florida is 49
inches. From table 14 the evapotranspiration loss for two represen-
tative basins averaged about 40 inches for the 3-year period. Based

Note. ET = P S-R- U
*Negligible
*Ground-water outflow for 1959 and 1960 assumed to be same as for November 1959 and
that for 1961 assumed to be the average for twb periods (table 17).

118

REPORT OF INVESTIGATIONS NO. 42

on these values the increased evaporation loss would be about 9
inches.

EVALUATION OF PROPOSED PLAN OF WATER CONTROL

A comprehensive plan of improvements proposed by the U. S.
Corps of Engineers (1961) provides for diversion canals and
flood-control conservation reservoirs in the Green Swamp area, and
in the upper Oklawaha, Peace, Hillsborough, and Withlacoochee
River basins, shown in figure 54. Green Swamp Reservoir, largest
of those included in the plan of improvement, would be located in
the Withlocoochee River basin near the center of Green Swamp.
The proposed Green Swamp Reservoir would provide for a total of
460,000 acre-feet of storage (134,000 acre-feet at conservation pool
level of 100 feet above msl and 326,000 acre-feet above the
conservation pool for flood control at level of 107 feet above msl).
The surface area of the flood-control pool would be about 61,000
acres.
The Southeastern Conservation Area (Johnson, 1961), also
designated the Lowery-Mattie Conservation Area (Corps of
Engineers, 1961), would be located in the southeast corner of the
Green Swamp area. This proposed water-conservation area would
cover about 46 square miles in three pools and provide for maximum
storage of about 72,000 acre-feet at pool levels ranging from 133.0
to 134.5 feet above msl.
Also within the Green Swamp area and included in the
comprehensive plan of improvement are the Little Withlacoochee
Reservoir, the Upper Hillsborough Reservoir, Big Creek upper and
lower diversion canals, and Lowery Canal.

REDUCTION OF FLOOD PEAKS IN THE
HILLSBOROUGH RIVER

The annual runoff to the Hillsborough River basin through the
Withlacoochee-Hillsborough overflow was 104,000 acre-feet for
1959 and 106,000 acre-feet in 1960. The flood-control pool of the
proposed Green Swamp Reservoir is capable of impounding the
total annual runoff contributed by the Green Swamp to the
Hillsborough River basin. For the purpose of computing the
effectiveness of the proposed Green Swamp Reservoir in reducing
flood peaks of the Hillsborough River at Tampa, the flood of March
1960 has been taken as a typical case. The maximum extent that

119

120 FLORIDA GEOLOGICAL SURVEY

the total Green Swamp area could reduce floods in the Hillsborough
River would be by the impoundment of all the discharge that drains
through the Withlacoochee-Hillsborough overflow channel al
station 39.
Hydrographs of mean daily discharge for Withlacoochee-
Hillsborough overflow, Hillsborough River near Zephyrhills, and
Hillsborough River near Tampa for the flood of March 1960 are
shown in figure 55. The hydrographs were plotted using mean
daily discharges at the gaging stations. The discharge at the
Tampa station was slightly regulated by the waterworks dam but
the effect is not apparent on the mean daily values of discharge.
The peak discharge at the Zephyrhills station, which is 2 miles
downstream from Blackwater Creek, occurred on March 18, the
same day as the peak from Blackwater Creek. The peak discharge
at Withlacoochee-Hillsborough overflow occurred on March 19 while

the peak for Hillsborough. River near Tampa was on March 21.
The flood peak at the Tampa station occurred about two days later
than that at the Withlacoochee-Hillsborough overflow and about 3
days later than that at the Zephyrhills station.
The gaging station near Tampa is in the upper pool at the
waterworks dam. In March 1960, the stage of the upper pool was
regulated between narrow limits by tainter gates and flashboards.
A stage-discharge relation was defined at 22nd Street, 0.5 mile
downstream from the dam, by measurements made during the
floods of 1959 and 1960. Mean daily discharges for the gaging
station at the dam were used with the stage-discharge relation to
compute the stage hydrograph for 22nd Street as shown in
figure 56.
| o __________________ ___ __ ^ ^ ^ -________

Hydrographs of computed mean daily stage of Hillsborough River
at 22nd Street,-Tampa, flood-of March 1960.

16

Figure 56.

FLORIDA GEOLOGICAL SURVEY

Mean daily discharges for Withlacoochee-Hillsborough overflow
were subtracted from the mean daily discharges for the Tampa
station two days later to synthesize the effective discharge that
would have occurred at the Tampa station if all the flow from
Green Swamp to the Hillsborough River had been impounded. This
adjusted discharge was used to compute the inferred stage
hydrograph for 22nd Street shown by the broken line in figure 56.
The difference between the two hydrographs on March 21 was 1.2
feet which indicates the maximum reduction in crest stage at 22nd
Street that would have occurred if the total flow from Green
Swamp to the Hillsborough River had been impounded. Similar
computations of the theoretical flood reduction at 22nd Street by
complete impoundment of the flow from Green Swamp were made
for the September 1960 flood. This flood crest would have been re-
duced by about 1 foot, approximately the same as that of the
March flood.
Other reservoirs and channel changes proposed for the
Hillsborough River basin (Corps of Engineers, 1961) would further
reduce the flood peaks at Tampa.

REDUCTION OF FLOOD PEAKS IN THE
WITHLACOOCHEE RIVER

The effect on the lower Withlacoochee River by storage of flood
discharge in the proposed reservoirs in Green Swamp was also
estimated on the basis of the March 1960 flood. Table A-1 of the
Corps of Engineers Comprehensive Report (1961) shows that the
total drainage area of the Withlacoochee River above Green Swamp
Reservoir is 328 square miles, and that above the Upper
Hillsborough Reservoir is 66 square miles or a total of 394 square
miles above the Trilby gaging station. Figure 57 shows the relation
between runoff in acre-feet and drainage area for the Withlacoochee
River basin for the flood period March 16 to April 20, 1960. From
this relation, the indicated flood runoff from a drainage area of 394
square miles was about 200,000 acre-feet during the March flood.
The allocated flood storage capacity of Green Swamp Reservoir is
326,000 acre-feet. Assuming that the flood-control pool would be
empty at the beginning of the flood period, the entire volume of
runoff from the basin above the reservoir could be impounded for
a flood greater than that of March 1960. This would be equivalent
to reducing the effective drainage area for uncontrolled flood runoff
above the Trilby gaging station to about 186 square miles (580

122

REPORT OF INVESTIGATIONS No. 42

600000

400,000

a,
f aoopoo

- 200,000
0
0
ao

- 100,000

50,000

100

200

500

1000

2000

Drainage area, in square miles
Figure 57. Relation between basin runoff and drainage area for
Withlacoochee River, March 16 to April 20, 1960.

square miles at gaging station minus 394 square miles above the
two reservoirs).
Peak discharges for the flood of March 1960 have been plotted
against drainage areas at gaging stations in the Withlacoochee
River basin as shown in figure 58. The peak discharge at
Withlacoochee-Hillsborough overflow was 1,880 cfs. From the
relation in figure 58, the drainage area that would produce a peak
discharge of 1,880 cfs for the March flood would be 100 square
miles. Effective drainage areas for the gaging stations downstream
from Withlacooche-Hillsborough overflow have been computed by
subtracting 100 square miles from the measured drainage areas of
each. The curve shown by the broken line in figure 58 represents
the theoretical relation of drainage areas to flood peaks that would
have prevailed if no flood discharge had been diverted from the
basin.

Holder 0

Croom
Trilby

Note:
Runoff at Trilby,
Croom, and Holder
adjusted to include
diversion from basin
Rerdell through Withlacoochee-
Hillsborough overflow.

Drainage area, in square miles
Figure 58. Relation between peak discharge and drainage area for
Withlacoochee River, flood of March 1960.

From the curve represented by the broken line in figure 58, the
peak discharge from a 186 square-mile drainage area would be
3,400 cfs. This discharge at the Trilby gaging station would occur
at gage height 15.4 feet, which is 4.0 feet lower than the crest
stage of March 1960.
Flood stages at the Croom station would be further reduced by
storage in Little Withlacoochee Reservoir (drainage area, 86 square
miles). The total reduction in crest stage for a flood equivalent to
that of March 1960 would be 1.7 feet at this station.
The reduction in crest stage by flood storage in reservoirs
proposed in Green Swamp would continue to decrease at points
further downstream on the Withlacoochee River. At the crossing
of State Highway 200 at the Holder station, reduction of crest stage
by storage in Green Swamp would be small. However, the Jumper
Creek Reservoir would provide additional storage for flood control
in the lower Withlacoochee River basin.

o

0 Eva

* *

124

REPORT OF INVESTIGATIONS NO. 42

EFFECTS OF WATER IMPOUNDMENT IN
GREEN SWAMP RESERVOIR ON GROUND-WATER LEVELS

Comparison of figures 31 and 54 show that the proposed Green
Swamp Reservoir is underlain at shallow depth by the Floridan
aquifer. A reconnaissance of the area indicated that limestone of
the aquifer crops out for about 6 miles along the north-south
portion of the proposed levee. The head created by the reservoir
will cause additional amounts of water to move through the aquifer
beneath the levee.
The principal factors controlling the underseepage are the
horizontal and vertical permeabilities of the materials beneath the
reservoir and the percentage of the reservoir area immediately
underlain by the Floridan aquifer.
Aquifer tests in adjacent areas indicate that the coefficient of
transmissibility varies considerably from point to point. The
coefficient of transmissibility in the reservoir area is estimated to
range from 125,000 gpd/ft to 500,000 gpd/ft. Significant amounts
of underseepage will probably occur along about 14 miles of the
north-south portion of the proposed levee because the predominant
direction of water movement is from the east to the west.
Underseepage will be greatest in the channel of the Withlacoochee
River because the channel is well incised into the aquifer.
The hydraulic gradients scaled from the piezometric maps
(figs. 35 and 36) were used to compute the existing wet and dry
period flow of ground water beneath the area of the proposed levee.
During the wet period (1959), the average elevation of the
piezometric surface beneath the 14-mile length of proposed levee
was about 95 feet, the average hydraulic gradient across the
proposed levee was about 2 feet per mile, and the estimated mean
daily underflow ranged from about 5 to 20 cfs. During the dry
period (1962), the average elevation of the piezometric surface
beneath the 14-mile length of proposed levee was about 89 feet,
the average hydraulic gradient across the proposed levee was about
2.6 feet per mile, and the estimated mean daily underflow ranged
from about 10 to 30 cfs.
In order to estimate future underflow it was assumed that the
amount of water that seeps into the limestone will raise the
piezometric surface to the same level as that of the conservation
pool (100 ft). If the impoundment occurred during a wet period,
then the piezometric surface would rise from 95 to 100 feet, the
gradient would increase from 2 to 7 feet per mile, and the estimated

125

FLORIDA GEOLOGICAL SURVEY

mean daily underflow would range from about 20 to 80 cfs. If the
impoundment occurred during a dry period, then the piezometric
surface would rise from 89 to 100 feet, the gradient would increase
from 2.6 to 13.6 feet per mile, and the estimated mean daily
underflow would range from about 40 to 150 cfs.
Seepage and evaporative losses from the shallow reservoir
indicate that the amount of water that would be available for
release during dry periods such as that in 1962 would probably be
small. The position of the reservoir with respect to contributing
recharge to the heavily pumped portions of the Floridan aquifer is
poor. However, benefits derived from the reservoir would be
increased base flow of the upper Withlacoochee and Hillsborough
rivers and reduction of flood crests.

EFFECTS OF WATER IMPOUNDMENT IN SOUTHEASTERN
CONSERVATION AREA ON GROUND-WATER LEVELS

The primary purpose of a plan for water impoundment in the
Southeastern Conservation Area (Johnson, 1961), also designated
the Lowery-Mattie Conservation Area (Corps of Engineers, 1961),
is to maintain and to increase recharge to the Floridan aquifer.
The three pools that would comprise the Southeastern Conservation
Area proposed by Johnson would cover about 46 square miles, with
pool levels ranging from 133 to 134.5 feet above msl. The pools
would overlie an area of high piezometric levels in the Floridan
aquifer. In this area, water normally seeps downward from the
nonartesian aquifer through a bed of clay (aquiclude) into the
underlying Floridan aquifer. Here, the water level in the
nonartesian aquifer and in surface-water bodies are above the
piezometric surface of the Floridan aquifer. The difference in levels
is caused by relative differences in the permeabilities of the
nonartesian aquifer, of the Floridan aquifer, and of the aquiclude.
The rate of seepage through the aquiclude is directly proportional
to the difference between the water levels; therefore, raising the
water table or lowering the piezometric surface will increase the
rate of seepage.
In order to evaluate the importance of the three conservation
pools, a comparison was made of seepage rates during wet and dry
periods in the vicinity of Lake Lowery with seepage rates that
would occur had the pools been at the proposed levels. The average
vertical permeability of the aquiclude was estimated and used as
the basis of computations of seepage rates for existing hydraulic

126

REPORT OF INVESTIGATIONS No. 42

:radients and for future hydraulic gradients. The vertical
permeability computed from the movement of 5 inches of water a
year through the 15 feet of aquiclude with a head difference of 2
feet is about 0.003 gpd/ft2.
During a wet period (November 1959), the average yearly
seepage from the eastern part of the area was determined to be
about 5 inches (table 14) when the level of Lake Lowery was about
134 feet and the piezometric surface was about 132 feet. During
a dry period (May 1962), the indicated yearly seepage from Lake
Lowery was about 21 inches when the level of Lake Lowery was
about 128 feet and the piezometric surface was about 120 feet. If
during May 1962 the water level in the Lowery pool had been
maintained at about 133 feet, the resulting gradient (13 feet)
would cause a yearly seepage rate of about 34 inches which is 60
percent greater than that computed for May 1962.
The piezometric surface will decline progressively in response
to increased pumping in the populated and industrialized areas
south of Green Swamp (see fig. 37). Therefore, maintaining high
water levels in the southeastern part of the Green Swamp area will
make additional water available for future recharge.

SIGNIFICANCE OF THE HYDROLOGY OF THE AREA

The Green Swamp area is unique because it is a headwaters
area for five major rivers and for part of the Floridan aquifer. The
proximity of the headwaters of the streams and their interconnec-
tions by swamps at relatively high elevation suggest that the area
can be used effectively for flood control and water conservation.
Because of the high piezometric surface, Stringfield (1936) and
others have inferred that high rates of recharge for the Floridan
aquifer occur on the Polk high in the Green Swamp area and that
ground water flows outward in all directions from the area. In
order to meet the demands of present and future water-use and
for flood prevention, a water-management plan was proposed to
utilize the Green Swamp area for impoundment of flood waters
and for increasing the amount of recharge to the Floridan aquifer.
Thus, the significance of the hydrology of this area in relation to
central Florida has been appraised on the basis of the findings of
this investigation.
In general, with other water-budget factors being equal, surface
runoff would be low in areas where high rates of ground-water
recharge occur. Therefore, comparison of streamflow from two

127

FLORIDA GEOLOGICAL SURVEY

areas, similar in other respects, would indicate the relative amount
of water recharged to the aquifers.
Table 7 shows that the total surface runoff during July, August,
and September 1960 from Pony Creek, a basin located on the Polk
piezometric high, was about 6 inches more than that from Horse
Creek, a basin located downslope from the Polk high, although the
rainfall on the Pony Creek basin was about 7 inches less. This
indicates a smaller ground-water storage capacity in the Pony
Creek basin than in the Horse Creek basin. Table 14 shows that
during the years 1959-61 surface runoff from the eastern basins,
which include the Polk high, was nearly the same as that from the
western basin although the rainfall was less. The conclusion derived
from comparing the data shown in Table 14 is that the rate of
ground-water recharge on the Polk high is about the same as that
in an area downslope from the Polk high.
Ground-water outflow from the Green Swamp area is almost
entirely via the Floridan aquifer. The net outflow over a significant
period of time is approximately equivalent to the average amount
of recharge to the aquifer during the period if there were no
appreciable change in ground-water storage. Table 14 shows that
the outflow is about 5 inches per year from the eastern part of the
Green Swamp area and about 3 inches per year from the western
part. Therefore, this infers that the eastern part contributes about
2 inches more recharge to the Floridan aquifer. The net ground-
water outflow from the Polk piezometric high (table 16) was
estimated to range from 181 to 258 cfs or about 3 to 4.2 inches
per year. Part of the outflow discharges into streams and swamps
in the western part of the Green Swamp area so that the net
amount that leaves as ground-water outflow probably ranges from
112 to 169 cfs, or about 1.8 to 2.6 inches per year (table 17).
Mineral content and calcium carbonate saturation with respect
to calcite in water in the Floridan aquifer implies that recharge is
about the same in the Green Swamp area as in other parts of central
Florida. The presence of low mineral content in water in the
interior of central Florida and high mineral content in water toward
the coasts (figs. 44 and 45) suggests a general movement of water
from the interior to the coasts. A comparison of the degree
(percentage) of calcium carbonate saturation of water with
respect to calcite in the Floridan aquifer throughout central Florida
shows that under-saturation occurs throughout much of central
Florida (fig. 43). Hem (1961, p. C-15) states that the degree of

128

REPORT OF INVESTIGATIONS No. 42

saturation should be lowest in recharge areas, and should increase
as water moves through the aquifer.
It would appear then that factors other than high recharge
rates contribute to the causes of the Polk high. It can be inferred
from geologic and hydrologic data that a relation exists between
the water movement and structural deformation in the Green
Swamp area. This is indicated at the surface by the parallel
linearity of ridges and surface drainage systems, and in the
subsurface by the presence of an anticline and related faults. Also
of importance is the relation between structural deformation and
subsequent solutional deformation indicated by the parallel linearity
of sinkhole lakes.
High piezometric levels in the southeastern part of the Green
Swamp area are believed to be the result of a relatively slow rate
of ground-water outflow which is probably caused by sand-filled
fractures, caverns, and sinkholes. These act as a natural grout
which decreases the transmissibility of the aquifer. Although the
coefficient of transmissibility of the Floridan aquifer is generally
high, it is variable, ranging from about 200,000 to 1,200,000 gpd/ft
(table 11). The lower value applies to the eastern part of the Green
Swamp area where the piezometric high exists.
Flood-control and conservation reservoirs proposed for the
Green Swamp area would provide a partial solution to the flood
problems in the lower Hillsborough River and lower Withlacoochee
River basins. Total impoundment in the Green Swamp area of a
flood equal to that of March 1960 would reduce the flood crest of
the Hillsborough River at Tampa by about 1 foot. Impoundment
of the March 1960 flood in reservoirs proposed for the Green Swamp
area would have reduced the flood crest of the Withlacoochee River
at the Trilby gaging station by about 4 feet and at the Croom
gaging station by about 1.7 feet. Reservoirs in the Green Swamp
area would be less effective in reducing flood stages further
downstream on the Withlacoochee River.
Impoundment of floodwaters. in the Green Swamp reservoirs
would probably have little effect on net ground-water outflow from
the Green Swamp area but would increase base flows downstream
from the reservoirs.
Impoundment of flood waters in the Southeastern Conservation
Area would increase the rate of seepage to the Floridan aquifer.
The rate of seepage would be more significant during dry periods
when the piezometric surface is lowered by pumping in the
developed areas south of the Green Swamp. Therefore, water

129

FLORIDA GEOLOGICAL SURVEY

storage in this area at the beginning of a dry period would become
more important as the demand for water increases.
Further drainage of the area could change the proportional
amounts of water disposed of by the various routes. The time of
concentration of water in stream channels would be decreased.
More water would be moved from the areas as streamflow. Water
would remain on the land surface for shorter periods and therefore
evapotranspiration would be decreased. Certainly if the water-table
in the whole area were lowered, this would effectively lower the
piezometric surface and decrease ground-water outflow from the
area. However, at present, the central and western parts of the
area are downgradient from the piezometric high and generally
are poorly drained both on the surface and subsurface. The area
is generally wet and runoff is high after intense rainfall because
the aquifers are always nearly full and the rate of ground-water
movement from the area is slow.
Although water management in the Green Swamp area would
not be the sole solution to the water problems in central Florida,
Green Swamp is hydrologically important and must be considered
in any overall plan of water management.

Anticline. An upfold or arch of rock strata, dipping in opposite directions
from an axis.

Aquiclude. A formation which, although porous and capable of absorbing
water slowly, will not transmit it fast enough to furnish an appreciable
supply for a well or spring.
Aquifer. A formation, group of formations, or part of a formation that will
yield water in usable amounts.
Artesian ground water. Water that is under pressure sufficient to cause it to
rise above the top of the aquifer in which it occurs.
Base flow. The discharge entering stream channels from ground water.
Clastic. Pertaining to fragmental material derived from pre-existing rocks
transported mechanically into its place of deposition, for example, sand
and clay.

Coefficient of permeability. The rate of flow of water, in gallons per day,
through a cross-sectional area of 1 square foot under a unit hydraulic
gradient at a temperature of 600 F.
Coefficient of storage. The volume of water an aquifer releases from or takes
into storage per unit surface area of the aquifer per unit change in the
component of head normal to that surface. In artesian aquifers it is re-
lated to the compressibility of the material comprising the aquifer and of
the water. In non-artesian aquifers it is primarily related to gravity
drainage and is approximately equal to specific yield.
Coefficient of transmissibility. The rate of flow of water, in gallons per day,
at the prevailing water temperature through each vertical strip of the
aquifer 1 foot wide having a height equal to the thickness of the aquifer
and under a unit hydraulic gradient.
Color. The color of water is due only to materials in solution. Color is de-
termined by comparison with standard colored disks that are calibrated in
units according to the platinum-cobalt scale.

134

REPORT OF INVESTIGATIONS No. 42 135

Confining bed. A bed which, because of its position and its impermeability or
low permeability relative to that of the aquifer, gives the water in the
aquifer either an artesian or subnormal head.

Confluence. The meeting or junction of two or more streams.
Diffuence. Flowing apart. A term used to describe a stream which branches
in a downstream direction.
Direct surface runoff. The runoff entering stream channels promptly after
rainfall.
Discharge. Flowing or issuing out. Also used to designate the volume of
water flowing past a cross section of a stream in a unit of time.
Double-mass curve. A plot of the cumulative values of one variable versus
the cumulative values of another.
Drainage area. The size of a drainage basin usually expressed in square
miles.

Drainage basin. An area enclosed by a topographic divide such that direct
surface runoff from precipitation normally would drain by gravity into
the river basin.
Drainage divide. The boundary line, along a topographic ridge, separating
two adjacent drainage basins.
Drainage system. A surface stream or a body of impounded surface water,
together with all surface streams and bodies of impounded surface water
that are tributary to it.
Effective precipitation. A weighted average of current and antecedent pre-
cipitation that is "effective" in correlating with runoff.
Evaporation. The process by which water becomes vapor at a temperature
below the boiling point, including vaporization from free water surfaces
and from land surfaces.

Evapotranspiration. Evaporation plus transpiration.
Fault. A fracture or fracture zone along which there has been displacement of
rock material on the two sides relative to one another parallel to the
fracture.
Ground water. That part of the subsurface water that is in the zone of
saturation.

Hydraulic conveyance. The water-carrying capacity of a stream channel.

Hydraulic gradient. As applied to an aquifer, it is the rate of change of
pressure head per unit of distance of flow at a given point and in a given
direction.

Hydrograph. A graph showing stage, flow, velocity, or other property of
water with respect to time.

Infiltration. See seepage.

FLORIDA GEOLOGICAL SURVEY

Instantaneous load. The quantity of dissolved material carried by a strearr
at the point and time indicated.
Marine. Of or belonging to or caused by the sea.
Mineral content. A summation of the individual values, in parts per million.
of the determined dissolved chemical constituent in the water.
Nonartesian ground water. Water in an aquifer that is unconfined.
Parts per million (ppm). A unit weight of a chemical constituent dissolved
in a million unit weights of water.
Percolation. The movement of water by gravity through the pores in a rock
or soil, excluding the movement through large openings such as caverns.
pH. An index of the acidity of water. A value of 7 is neutral. Values above
7 indicate alkalinity-values below 7, acidity .
Piezometric surface. The level to which water will rise in tightly cased wells
that penetrate a given aquifer.
Potential natural water loss. The maximum water loss that could occur natu-
rally in a basin with optimum or full moisture supply and native vegetation.
Recharge (of ground water). Intake. The processes by which water is ab-
sorbed and is added to the zone of saturation. Also used to designate the
quantity of water that is added to the zone of saturation.
Retention. The part of storm rainfall which is intercepted, stored, or delayed,
and thus fails to reach the concentration point by either surface or sub-
surface routes during the time period under consideration.
Runoff. That part of the precipitation that appears in surface streams,
having reached the stream channel by either surface or subsurface routes.

Runoff in inches. The depth to which an area would be covered if all the
runoff from it in a given period were uniformly distributed on its surfaces.

Seepage (infiltration). Percolation of water through the earth's crust, or
through the walls of large openings in it, such as caves or artificial exca-
vations.

Specific conductance. Specific conductance is the measure of the capacity
of water to conduct an electric current. It varies with the concentration
and degree of ionization of the different constituents in solution. It may be
used to estimate the mineral content but does not indicate the nature of,
or the relative amounts of, the various mineral constituents.

Specific yield. The ratio of the volume of water that will drain from the
saturated material of the aquifer- to the volume of the material, ex-
pressed in percent.

Streamflow. The actual discharge of surface streams. It includes runoff
modified by artificial causes.

Surface water. Water that occurs above the surface of the ground.

136

REPORT.OF INVESTIGATIONS NO. 42

137

Time of concentration. The time .required for the water to flow from the
farthest point on the watershed to a gaging station or to another specified
point.
Transpiration. The process by which water vapor escapes from a living plant
and enters'the atmosphere.
Water loss. The difference between the average precipitation over a drainage
basin and the runoff adjusted for changes in storage and for interbasin
movement of ground water. The basic concept is that water loss is equal
to evapotranspiration; that is, water that returns to the atmosphere and
thus is no longer available for use in the area. However, as used in this
report, the term applies to differences between measured inflow and outflow
even where part of the difference may be seepage.
Zone of saturation. The zone in which the permeable rocks are saturated with
water under pressure equal to or greater than atmospheric.

Report of Investigations No. 42

62"5' 10 05 82*00' 55' 50 45 40' 35' 8i130

EXPLANATION
SBoundary of Green Swamp orea V Rainfall station
.- 5 Well and well number I Surface water data >-
collection point.
z=

Area of artesian flow
Extent and distribution of flow areas vary with fluctuations /
of the piezametric surace, paoieulmly in areas of heavy
pumping. Relatively small oreas of artesian flow are not.
included immediately adjacent to and paralleling the / !
coast and many of the major rivand springs.
P f -- F

267
0 10 20 30 40 50 miles

Taken from Map Series No4 by H.G. Healy, 196).

84 83 82* 81" 80*

Figure 33. Map of Florida showing contours on the pizometric surface of the
Floridan aquifer. 1961.